What is the backfire effect?

When a core belief is challenged with contradicting evidence, people sometimes dig in and believe it even more strongly.

The mechanism is identity-defence: a belief tied to who we are feels like part of us, so an attack on it is processed as an attack on the self. Instead of updating, we spend mental effort generating counter-arguments and rationalisations — and that effort strengthens the belief, leaving us more entrenched than before.

Example: Showing someone a thorough fact-check that debunks a rumour they're invested in can leave them more convinced of the rumour, because they marshalled reasons to dismiss the correction and reinforced the original belief in doing so.

Tip: Facts alone rarely move identity-linked beliefs. Lowering the stakes ("you're not stupid for having believed this") often works better than piling on more evidence.