Confirmation bias is the tendency to notice, remember and interpret information in a way that confirms what we already believe, while quietly ignoring whatever contradicts it. It isn't bad intent; it's a mental shortcut that spares us the fatigue of rethinking everything from scratch.
An everyday example: if you've decided a colleague is indifferent, you'll vividly recall every time they were slow to reply and skip right over the times they helped you. The same happens with ourselves: if we believe "I'm not good enough," we unconsciously gather every piece of evidence that supports it and dismiss anything that doesn't.
Psychologically this matters because our beliefs tend to become self-fulfilling. When we see only what confirms our fear or our self-criticism, our picture of the world and of ourselves grows narrower and more rigid. Relationships suffer, because we rarely change our minds even when the other person gives us reason to.
The first step is simple awareness: asking "what evidence would change my mind?" and actively looking for it. In therapy, much of the work is gently examining our automatic thoughts. If you'd like to build more flexible thinking patterns, take a look at our services.