Clear Thinking

Parrish, who runs Farnam Street, argues that most decision quality is determined before any decision is consciously made, because ordinary moments are handled by default reactions that people do not notice as choices. His four defaults are the emotion default, reacting to feelings rather than reasons; the ego default, protecting self-image; the social default, conforming to the group; and the inertia default, preferring what already exists.

His countermeasures are strengths that must be built in advance rather than summoned in the moment: self-accountability, self-knowledge, self-control and self-confidence. He then gives operating rules, including creating space between stimulus and response by requiring a delay, setting rules for yourself in advance rather than deciding in the moment, removing yourself from environments that trigger the defaults, and managing the conditions that degrade judgement, meaning hunger, fatigue, emotion and social pressure.

The decision process he sets out covers defining the problem correctly before considering solutions, generating genuinely different options rather than variations on one, setting the criteria before evaluating, using a pre-mortem, and deciding how much time a decision deserves based on whether it is reversible.

The book is short and practical. It is synthesis rather than research, and readers familiar with Kahneman, Munger, Tetlock and the Heaths will find little that is new in substance. Parrish's contribution is compression and the specific framing of defaults as the thing to manage, which is a useful reorganisation of familiar material. There is no empirical work of his own.

Founder of Farnam Street and host of The Knowledge Project podcast; previously an analyst for a Canadian intelligence agency.

The Great Mental Models collects the reasoning tools investors borrow from other disciplines - inversion, second-order effects, margin of safety, the map and the territory, circle of competence - and gives each a worked example rather than a slogan. Clear Thinking covers the practices around those models: noticing that a decision is being made at all, and setting rules before the moment arrives.

Farnam Street