The Danger of "Expectation Bias"
Spanair flight 5022 crashed in 2008 because of "expectation bias". The pilots confirmed the flaps were set when they weren't set. The pilots looked and confirmed they were set but they were never set at all. They were in essence "looking without seeing."
"Expectation bias" can lead to one interpreting results incorrectly that conforms to their hypothesis and overlook information that argues against it. It is a person expecting to hear what they want to hear rather than what actually may be occurring.
Sometimes what we can expect to see we do not truly see
But we can imagine to see what we do not see
So in assuming to see what we expect to see we end up not seeing what we should truly see
And in seeing what we expect to see
It causes us to neglect to see
What we should truly see