New Phrases
Mental Models – by defmacro
January 9, 2018

These are some mental models I find useful. They’re rooted in decades
of experience of thousands of experts – a modern equivalent of folk
wisdom. Mental models are useful to quickly and correctly reason about
seemingly intractable problems. They require quite a bit of intuition
to properly internalize, but once you’ve internalized them they’re
relatively easy to apply. They’re also easy to forget in the moment –
use this post as a checklist when thinking about complex problems.

This is a living document. Instead of creating an exhaustive list on
day one, I will add models as they arise (and as I discover new ones).


  • The small-improvements method – the observation that
    psychologically frequently making small incremental improvements is
    a better approach than attempting to fix big looming problems once.
  • The just-get-started method – Joel Spolsky’s observation that
    just starting to work on a small, concrete, finishable problem puts
    your consciousness in a productive state.
    Corollary: Just do something concrete. Anything. Do your
    laundry, or dust the counters, or add a single unit test. Just do
  • The top-five-problems method – Richard Hamming’s algorithm for
    doing important work. Periodically ask yourself: “what are the top
    five most important problems in my field (and life), and why am I
    not working on them?”
    Corollary: What are the top five most important problems in your
    field (and life), and why aren’t you working on them?
  • The LRU prioritization method – since you can only work on one
    problem at a time, it’s usually sufficient to pick the most
    important problem, work on that, and ignore everything else. This
    method also works with organizing most things (from email to
    physical possessions).
  • The teaching method – Richard Feynman’s observation that teaching
    the basics is an excellent method for generating profound new ideas,
    and for putting consciousness in a productive state.
    Corollary: If you’re stuck, put yourself in a position where you
    have to teach someone the basics.
  • Planning fallacy – the observation that humans are overly
    optimistic when predicting success of their
    undertakings. Empirically, the average case turns out to be worse
    than the worst case human estimate.
    Corollary: Be really pessimistic when estimating. Assume the
    average case will be slightly worse than the hypothetical worst
    Corollary: When estimating time, upgrade the units and double
    the estimate (e.g. convert “one week” to “two months”).
  • Forcing function – an external, usually social, constraint that
    increases the probability of accomplishing a set of tasks.
    Example: Pair programming.

Hypothesis evaluation

  • Efficient market hypothesis – the state of any given issue in the
    world is roughly as close to optimal as is currently possible.
    Corollary: It’s unlikely that the status quo can be easily
    improved without significant resources.
    Example: Cucumber juice probably doesn’t cure cancer.
    Example: The iPhone app you wrote in a weekend probably doesn’t
    double the phone’s battery life.
  • Statistical mechanics – probabalistic systems that follow certain
    laws in the long run can have perturbations that diverge from these
    laws in the short run.
    Corollary: Occasionally the status quo can be easily improved
    without significant resources (but it is unlikely that you found
    such an occassion).
    Idiom: In the short run the market is a voting machine, but in
    the long run it is a weighing machine.
    Idiom: If an economist saw a $100 bill on a sidewalk they
    wouldn’t pick it up (because if it were real, it would have been
    picked up already).
  • Base Rates – you can approximate the likelihood of a specific
    event occuring by examining the wider probability distribution of
    similar events.
    Example: You’re evaluating the probability of success of a given
    startup. Ask yourself, if you saw ten similar startups a year, how
    many of them are likely to succeed?
    Example: You caught an employee stealing, but they claim they
    need money to buy medication and it’s the first time they’ve ever
    stolen anything. Ask yourself, if you saw ten employee thefts a
    year, how many of them are likely to be first offences?
    Note: This method is especially useful to combat optimism and
    overconfidence biases, or when evaluating outcomes of events
    you’re emotionally close to.
  • Emic vs etic (aka inside vs outside view) – two perspectives you
    can choose when evaluating persuasive arguments. The inside view is
    time consuming and requires you to engage with the arguments on
    their merits. The outside view only requires you ask “what kind of
    person does sincerely believing this stuff turn you into?”
    Corollary: You can usually predict correctness of arguments by
    evaluating superficial attributes of the people making them.
    Example: If someone is wearing funny clothes, purports to know
    the one true way, and keeps talking about the glorious leader, you
    can usually dismiss their arguments without deeper examination.
    Warning: This method usually works because most kooky people
    aren’t innovators, but will misfire in important situations because
    many innovators initially seem kooky.

Decision making

  • Inversion – the observation that many hard problems are best
    solved when they’re addressed backward. In other words figure out
    what you don’t want, avoid it, and you’ll get what you do want.
    Corollary: Find out how people commonly fail doing what you do,
    and avoid failing like them.
    Example: If you want to help India, ask “what is doing the worst
    damage in India and how can we avoid it?”
    See also: Failure mode.
  • Bias for action – in daily life many important decisions are
    easily reversible. It’s not enough to have information – it’s
    crucial to move quickly and recover if you were wrong, than to
    deliberate indefinitely.
    Idiom: One test is worth a thousand expert opinions.
    Idiom: The best thing you can do is the right thing, the next
    best thing is the wrong thing, and the worst thing you can do is
    Note: The best people do this naturally, without brooding, and
    with a light touch.
  • Expected value – a simple model for evaluating uncertain events
    (multiply the probability of the event by its value).
    Corollary: Sometimes you’ll have to estimate probabilities when
    it feels really hard to do.
    Example: Chance of winning NY lotto is 1 in 292,201,338 per
    game. Let’s say the grand prize is $150M and ticket price is
    $1. Then the expected value is roughly $0.5. Since $0.5 < $1, the
    model tells us the game isn’t worth playing.
    Warning: Looking at expected value often isn’t enough. You
    need to consider utility to make good decisions.
    See also: Techniques for probability estimates, shut up and
    , scope insensitivity.
  • Marginal utility – the change in utility from the change in
    consumption of a good. Marginal utility usually diminishes with
    increase in consumption.
    Example: The first car in your garage improves your life
    significantly more than the second one.
    Example: Because utility loss from losing a dollar is negligible
    relative to utility gain from winning NY Lotto at ridiculously low
    odds, it might be worth buying a ticket even at negative expected
    value (but seriously, don’t).
    Corollary: Think through your utility function carefully.
  • Strategy and tactics – empirically decisions tend to fall into
    one of two categories. Strategic decisions have long-term, gradual,
    and subtle effects (they’re a gift that keeps on giving). Tactical
    decisions are encapsulated into outcomes that have relatively quick
    binary resolutions (success or failure).
    Example: Picking a programming language is a strategic decision.
    Example: Picking a line of reasoning when trying to close a sale
    is a tactical decision.
    Corollary: Most people misuse these terms (e.g. “we need a
    strategy for this meeting”).


  • IQ, RQ, and EQ – respectively, intelligence quotient
    (assessment of the mind’s raw horse power), rationality quotient
    (assessment of how well the mind’s models map to the real world; a
    measure of efficiency of the IQ’s application to real problems), and
    emotional quotient (ability to recognize and label emotions).
    Corollary: brilliant people can be jerks and kooks, empathic
    people can have wacky ideas about reality, and effective people can
    have average intelligence.
  • Structure and agency – the observation that human behavior
    derives from a balance of internalized cultural patterns and
    capacity to act independently. The interaction of these two
    properties influences and limits individual behavior.
    Corollary: Pay attention to the need for structure and
    independence in each individual.
    Corollary: Put a structure in front of even the most
    independent-minded people, and they’ll internalize it.
    Corollary: People often behave the way they believe their role
    requires them to (as opposed to the actual requirements of the
    Corollary: Pay attention to how people perceive their own
    roles, and break their expectations with caution.
  • Social status – the observation (particularly in improv) that
    social status is so important to humans, that modeling status alone
    results in extremely realistic performances.
    Corollary: Pay attention to how people perceive their own
    status, and break their expectations with caution.
    See also: Self-serving bias.
  • Controlled vulnerability – the observation that humans are
    attracted to confidently expressed vulnerability in others but are
    scared to be vulnerable themselves.
    Corollary: Humans feel strong attraction towards others who
    confidently display vulnerability.
    Corollary: Humans feel a strong desire to reciprocate
    vulnerability. Vulnerability expression by others gives them a
    sense of safety to express themselves, followed by a feeling of
    relief and a strong bond with the counterpary.


  • Mere-exposure effect – an observation that humans tend to develop
    a preference for things, people, and processes merely because they
    are familiar with them. This effect is much stronger than it
    initially seems.
    Corollary: Merely putting people in a room together repeatedly,
    giving them a shared direction, symbology, and competition will
    create a group with very strong bonds.
    See also: In-group favoritism.


  • Story arc – human beings are wired to respond to storytelling. A
    story arc is a way to structure ideas to tap into this response,
    typically by describing a change in the world.
    Example: Once upon a time there was ___. Every day, ___. One
    day ___. Because of that, ___. Because of that, ___. Until
    finally ___.
  • Writing well – use arresting imagery and tabulate your thoughts
    precisely. Never use a long word where a short one will do. If it’s
    possible to cut a word out, always cut it out. Don’t hedge – decide
    what you want to say and say it as vigorously as possible. Of all
    the places to go next, choose the most interesting.
  • Charitable interpretation – interpreting a speaker’s statements
    to be rational and, in the case of any argument, considering its
    best, strongest possible interpretation. Charitable interpretation
    makes conversations (and relationships) go better.
  • Nonviolent Communication (aka NVC) – a communication framework
    that allows expressing grievances and resolving conflicts in a
    non-confrontational way. Structuring difficult conversations as
    described in NVC makes the process dramatically less painful. NVC
    contains four components: (1) expressing facts, (2) expressing
    feelings, (3) expressing needs, and (4) making a request.
    Example: You didn’t turn in the project yesterday. When that
    happened I felt betrayed. I need to be able to rely on you to have a
    productive relationship. In the future, could you notify me in
    advance if something like that happens?


  • Global utility maximization – our innate sense of fairness is
    often unsatisfied, and attempting to satisfy it can occasionally
    cause much grief in exchange for little gain. It’s much better to
    optimize for the needs of the many, not for an idealistic notion of
    Corollary: There are times when it makes sense to be unfair to
    the individual in the interest of the common good.
    Example: It makes sense to fire an underperforming employee who
    has valid excuses for their poor performance.
    Idiom: It is the greatest happiness of the greatest number that
    is the measure of right and wrong.
  • Tragedy of the commons – a set of circumstances where individuals
    acting independently in a reasonable manner behave contrary to the
    common good.
    Example: Tourists taking small artifacts from popular
    Corollary: Governance is necessary to preserve the common good.
  • Front page test – an ethical standard for behavior that
    evaluates each action through the lens of the media/outside world.
    Example: What would happen if HN found out we’re mining our
    users’s IMs?
    Warning: Incentivizes extreme risk aversion, often without
    appropropriate consideration for potential gain.
  • Reasonable person principle – a rule of thumb for group
    communication originated in CMU. It holds that reasonable people
    strike a suitable balance between their own immediate desires and
    the good of the community at large.
    Corollary: Fire people that are offensive or easily
    offended. (It usually turns out that people who possess one of these
    qualities, possess both.)
    Note: unreasonable persons can be extremely valuable in greater
    society (e.g. journalists, comedians, whistleblowers, etc.), but
    usually not in small organizations.
  • Overton window – the range of ideas a particular group of people
    will accept. Ideas range in degree of acceptance from policy, to
    popular, sensible, acceptable, radical, and unthinkable.
    Corollary: you need to be sensitive to the overton window when
    presenting the group with cultural changes.
  • Political capital – the trust and influence a leader wields with
    other people. Political capital increases when you make other people
    successful and decreases when you make unpopular decisions.
    Corollary: Spend political capital carefully.

Product design

  • Target market – a predicate that partitions new leads into
    opportunities and distractions. A good target market function is
    terse, has a discoverable domain, and has a well defined probability
    of close in a specific time bound.
    Example: Anyone who has a Cisco password has a 50% probability
    of close within 30 days.
  • Internal press release – you start developing a product by
    writing an internal press release first, explaining to target
    customers why the product is useful and how it blows away the
    competition. You then test it against potential users (it’s much
    easier to iterate on the press release than the product).
    Corollary: If the press release is hard to write, then the
    product is probably going to suck.
  • Quantum of utility – a rule of thumb for launching the product. A
    product possesses a quantum of utility when there is at least some
    set of users who would be excited to hear about it, because they can
    now do something they couldn’t do before.
    Note: “Launch” can be defined as a private beta, or even giving
    the product to a friend. The point is to get it into the hands of
    someone who’s not in the building as soon as possible.
  • Worse is better – a design philosophy which states that solving
    the customer’s problem and leaving unpolished rough edges
    empirically outperforms “beautiful” products.
    Example: Lisp Machines vs C/Unix.
    See also: Worse is worse.
  • Kano model – a model for categorizing possible features to
    optimize resource allocation. Essentially partitions the product
    into gamechangers, showstoppers, and distractions.
    See also: How to build great products.


  • Five forces – a model for analyzing the competitive intensity and
    therefore attractiveness of an industry. The five forces are: threat
    of new entrants, threat of substitutes, bargaining power of buyers,
    bargaining power of suppliers, and industry rivalry.
    Note: this is essentially a base rate estimation model for
    companies in an industry.
  • Power of defaults – the observation that people favor the
    familiar over novel places, people, things, and processes.
    Corollary: Overcoming the familiarity heuristic at scale
    requires enormous activation energy unavailable to startups.
    Corollary: It is dramatically easier to capture mindshare before
    people’s minds are made up, than to change their mind later.
  • Economies of scale – the advantages due to size or scale of
    operation, where cost per unit decreases with increasing scale.
    See also: Network effects, brand equity, first mover
  • Price/performance curve – the observation that the price of
    important technology drops and performance improves over time.
    Example: Moore’s Law.


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