Why do we notice only the evidence that proves us right?

Because your brain is better at defending ideas than testing them. Confirmation bias is the tendency to search for, interpret, favour and remember information in a way that confirms what you already believe. It isn't lying; it's the way we look.

The classic demonstration is a simple game. In 1960, psychologist Peter Wason told people that the numbers 2, 4, 6 fit a secret rule and asked them to find it by proposing other triples. Someone who guessed "add two each time" would test 11, 13, 15, hear "yes", and grow more confident, instead of trying something like 11, 12, 19 that could prove the guess wrong. The real rule was simply "any ascending sequence", and many people never found it. Wason coined the term confirmation bias. Later researchers added a fair nuance: in many real problems, testing examples that fit your idea is actually a sensible strategy. It only misleads when the truth is broader than your guess.

Beliefs also bend how we read evidence. At Stanford, people with strong views on the death penalty read descriptions of studies that were entirely fictional. Almost all ended up back at their original belief, praising the details that suited them and dismissing the rest. We hold unwelcome evidence to a higher standard.

There's good news, though. The feared "backfire effect", where correcting a false belief makes it stronger, has widely failed to replicate, and factual corrections often help. Our minds are stubborn, not sealed.