This is one of the most common and dangerous ones, and is related to our beliefs.It leads us to ‘confirm’ what we already know, believe or suspect when any new piece of data comes in the light. If there is an alternate or conflicting piece of evidence, we tend to sideline, ignore or discount it. If it is too powerful to be ignored, it makes us experience cognitive dissonance.
People unconsciously seek to confirm their existing beliefs. To expand one's mind or prove any hypothesis, one should be looking for pieces of evidence that disprove it.