Why do we bend our beliefs to fit what we've already done?

We bend our beliefs to fit our actions because holding two clashing thoughts at once is genuinely uncomfortable, and changing a belief is often easier than undoing a deed. The psychologist Leon Festinger called that discomfort cognitive dissonance. He proposed that we strive for inner consistency, and when we fall short we rationalise, pay attention to the evidence that suits us, and avoid the evidence that doesn't.

His most famous test, in 1959, was wonderfully boring. Students at Stanford spent an hour turning pegs a quarter-turn and doing other tedious tasks. Then some were paid $20, others just $1, to tell the next participant it had been interesting. Later, the $1 group rated the task more positively than the $20 group. The explanation: $20 was a good enough reason to fib, but $1 wasn't, so those students resolved the clash between "I said it was fun" and "it was dull" by deciding it hadn't been so dull after all.

Aesop described the same move long ago: a fox who can't reach some grapes declares they're sour anyway.

Festinger's other famous story deserves more caution. He and colleagues secretly joined a small group that expected a world-ending flood on 21 December 1954, and reported that the most committed members grew even more devoted when it didn't come. But the researchers took part in the events themselves, and a 2025 archival study accused the authors of fabricating parts of the story.