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
- 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.
- 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
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.
- 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
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
multiply, 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
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
- 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
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
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.
- 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.
Collected from: http://www.defmacro.org/2016/12/22/models.html