Confirmation Bias is when you believe something is likely to be true, then you notice it occurring "in the wild" all the time. You'll tend to miss, ignore, or downplay instances when your belief was wrong or incorrect. This happens unconsciously. Confirmation bias is cyclical. This reinforces your belief that it's true, which starts the cycle all over again.
<aside> ⚠️ BEWARE OF CONFIRMATION BIAS
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I believe confirmation bias plays a large part in prejudice and hate in our world. In a "whole population" sample, it's relatively trivial to find case examples that suit your beliefs, then extrapolate those examples to the whole population - even if mathematically those examples are exceptions to the standard.