6 ideas
To choose between two options, rank cues by their validity, then decide based solely on the single most valid cue that discriminates between them, ignoring all remaining cues. This one-reason decision-making stops searching as soon as one cue points to an answer rather than integrating and weighing all available information.
A heuristic is not rational or irrational in itself; its performance depends on how well its structure matches the structure of the environment in which it operates. Rationality lives in the fit between mind and world, so the right test of a strategy is its success in real environments, not its conformity to logical or probabilistic axioms.
Simple heuristics using few cues often predict more accurately than complex models that use all available information and optimize parameters. The reason is that complex models overfit noise in past data, while frugal strategies that ignore information generalize better to new cases.
When choosing which of two objects scores higher on some criterion, if you recognize one and not the other, infer that the recognized one ranks higher. This exploits the fact that recognition is often systematically correlated with the criterion, so partial ignorance can itself become a source of accurate inference.
American students judging which of two German cities was larger sometimes outperformed German students, because the Americans recognized fewer cities and could apply the recognition heuristic, while the Germans recognized too many to use it. This 'less-is-more effect' shows that having less knowledge produced more accurate judgments.
Rather than a single all-purpose reasoning system, the mind is viewed as a collection of specialized, fast-and-frugal heuristics, each suited to particular tasks and environments. Intelligent behavior comes from selecting the right tool for the situation, not from applying one universal optimization procedure.