Seven pillars
Mental models
A mental model is a compact, reusable representation of how some part of the world works, applied to reason about a new situation faster and more reliably than working it out from scratch each time.
The models below are the ones that change decisions rather than just describe them. Each page gives the definition first, then where the model applies, where it breaks, and a worked example you can check. Concepts are grouped by pillar — decision-making, incentives, information, biases, systems, risk, and the general thinking toolkit.
Concepts
Decision-Making Under Uncertainty
Expected Value
The probability-weighted average that tells you which bets to take — and the four situations where following it misleads you.
Cognitive Biases & Judgment
Sunk Cost Fallacy
Why does money you can never get back keep steering decisions it has no claim on?
FAQ
What is a mental model in simple terms?
A mental model is a reusable idea about how something works, carried from one situation to the next. Expected value, opportunity cost, and feedback loops are examples. You keep the shape of the reasoning and swap in new details, instead of thinking every problem through from nothing.
What is the difference between a mental model and a cognitive bias?
A mental model is a tool you apply deliberately to reason better; a cognitive bias is a systematic error your judgment makes on its own. Models are picked up and used, biases are detected and corrected. Some pages here cover models, others cover the biases that distort them.
How many mental models do you actually need?
Far fewer than most lists suggest. A small set covering probability, incentives, second-order effects, and your own known biases handles most decisions. Breadth matters less than recognising which model a situation calls for, which comes from repeated use rather than from collecting more names.