We seek out information that fits with what we want to hear

Hope has a wonderfully flexible stopping rule. It can extend a trial, shrink a sample and declare Tuesday an outlier before lunch.

A favoured campaign needs one more week for the signal to mature. A disliked idea has already failed by lunchtime. Investors refresh reassuring news and postpone the awkward analysis. Managers interpret vague employee feedback as proof that the change is settling in. A product champion calls weak adoption “early learning” while an unloved experiment gets buried for missing its first target. The evidence threshold stretches towards whatever answer feels nicest. Nobody has to falsify a number when they can keep renegotiating what the number means.

Write the rules before dipping the strip: duration, success measure, failure signal, reasons to extend. Keep a record of the rule changes and require the same generosity for competing ideas. Give the evidence to someone who would enjoy the opposite result. Preference is inevitable and sometimes useful—it keeps effort alive during uncertainty. It just should not own the stopwatch. A decision process that only produces evidence for the sponsor’s favourite is expensive reassurance, however many charts attend. The moment “inconclusive” always means “not yet flattering”, the experiment has become emotional support with a dashboard.

Behavioural principles

Behavioural ideas at play in this post

Short, plain-English explanations of the principles behind this post, with links to related books and examples in the archive.