What is confirmation bias, why do our minds do it, and what does it look like in practice?

The tendency to seek, notice and remember evidence that supports what you already believe, while overlooking or discounting evidence that doesn't.

The mechanism is that holding a belief is comfortable and revising one is costly. Once a belief is in place, the brain treats it as the default and grades incoming information against it: confirming evidence is accepted easily, contradicting evidence is scrutinised harshly or filtered out before it registers. We're effectively building a case for a verdict we've already reached, not testing a hypothesis.

Example: You decide a new colleague is unfriendly. Afterwards you vividly notice every curt reply, and the times they were warm or helpful slide past unremembered — so the evidence "piles up" in favour of a conclusion you formed on day one.

Tip: The antidote is to deliberately go looking for what would prove you wrong. If you only ever find agreement, you may simply not be looking for disagreement.