SmartStops comments:  If you haven’t learned yet what behavior finance has proven it’s that “Confirmation bias” is that this fundamental principle applies to investors in notable ways. Because investors seek out information that confirms their existing opinions and ignore contrary information that refutes them, they may skew the value of their investing decisions based on their own cognitive biases. This psychological phenomenon occurs when investors filter out potentially useful facts and opinions that don’t coincide with their preconceived notions.

From an excellent article written by Barry Ritholtz/ Ben Carlson of a Wealth of Common Sense,  we learn too that :  “nothing has aided the persistence of falsehood, and the evils resulting from it, more than the unwillingness of good people to admit the truth when it was disturbing to their comfortable assurance. Always the tendency continues to be shocked by natural comment and to hold certain things too “sacred” to think about.”\
Confirmation bias is a hell of a drug:
Man seems to come into this world with an inalterable belief that he knows best and that he can make others think as he does by force. Those who read history tend to look for what proves them right and confirms their personal opinions. They defend loyalties. They read with a purpose to affirm or attack. They resist inconvenient truth since everyone wants to be on the side of the angels. Just as we start wars to end all wars.
If a man reads or hears a criticism of anything in which he has an interest, watch whether his first question is as to its fairness and truth. If he reacts to any such criticism with strong emotion; if he bases his complaint on the ground that it is not “in good taste” or that it will have a bad effect, in short, if he shows concern with any question except “Is it true?” he thereby reveals that his own attitude is unscientific.
The inability to change one’s mind is also a progress-stopper:

Likewise if in his turn he judges an idea not on its merits but with reference to the author of it; if he criticizes it as “heresy”; if he argues that authority must be right because it is authority; if he takes a particular criticism as a general depreciation; if he confuses opinion with facts; if he claims that any expression of opinion is “unquestionable”; if he declares that something will “never” come about or is “certain” that any view is right. The path of truth is paved with critical doubt and lighted by the spirit of objective inquiry. To view any question subjectively is self-blinding.”