The figures in this group fall into two families that rarely meet. One is a set of paradoxes that forced decision theory to change. The other is a set of sayings, most of them wry, that record what practical people learned about deciding. Both are compressed arguments, and both have lasted because they are easier to remember than the theory around them.
Paradoxes as stress tests
The paradoxes are the history of rational choice theory told through its failures. The St Petersburg Paradox showed in the eighteenth century that expected value alone could not describe what anyone would pay for a gamble, and Bernoulli's answer introduced utility. The Allais Paradox and the Ellsberg Paradox showed in the 1950s and 1960s that people treat certainty and known odds differently from what expected utility allows, which led to prospect theory and the study of ambiguity. Newcomb's Problem still divides philosophers into two camps over how to act when your choice has already been predicted.
The older paradoxes are about deciding at all. Buridan's Ass cannot choose between two equal bales of hay, the Sorites Paradox asks where a heap begins, and Bonini's Paradox warns that a model detailed enough to explain a system becomes as hard to understand as the system. Each marks a place where a clean rule meets a messy case.
Sayings about deciding
The second family is practical and often funny. Falkland's Rule, from the seventeenth century, says that when it is not necessary to decide, it is necessary not to decide. Voltaire's perfect is the enemy of good argues the other way, against delay. Mencken's Law warns that every complex problem has a solution that is neat, plausible and wrong, and Hofstadter's Law says things always take longer than expected, even when you allow for Hofstadter's Law.
Some sayings describe the decider's own position. Nobody Ever Got Fired for Buying IBM records that people choose what is easiest to defend if it fails. The Maes-Garreau Law observes that optimistic predictions about technology tend to land within the predictor's lifetime. Segal's Law, that a man with two watches is never sure of the time, catches the cost of conflicting information.
Where it applies
The paradoxes are useful to anyone who builds models of choice, in economics, insurance, policy or artificial intelligence, because each shows a place where a tidy theory predicts badly. The sayings are useful in meetings. Falkland's Rule is a defence against premature decisions, Voltaire's adage against endless ones, and knowing both is the point. The IBM saying explains a great deal of procurement, and the Maes-Garreau Law is worth recalling whenever a forecast of transformation arrives with a date attached.
Where it is argued over
The paradoxes are mostly settled as puzzles but live as philosophy: Newcomb's problem has no agreed answer, and the Allais result is read by some as irrationality and by others as proof that the theory had the wrong idea of preference. The self-help entries carry the group's sharpest dispute. Hill's Decision Rule, that successful people decide quickly and revise slowly, runs against research on updating beliefs in proportion to evidence, and the Decision-as-Destiny Principle rests on testimony selected from people who succeeded.
Why it is worth knowing
Pairs of sayings in this group contradict each other on purpose, like Falkland and Voltaire, and together they describe a judgement no rule can make for you: when to decide and when to wait. The paradoxes teach humility about formal theories of choice, since each was once a counterexample that the best theory of its day could not absorb. Between them, the two families keep formal reasoning honest and practical reasoning alert.
The entries behind this essay: Figure in Decision-making & Reasoning. Every subject has its essays on the essays page.