Confirmation bias (also known as positive bias) is the tendency to search for, interpret, favor, and recall information in a way that confirms or strengthens one's prior personal beliefs or hypotheses [1]. For example, one might test hypotheses with positive rather than negative examples, thus missing obvious disconfirming tests.

“I had, also, during many years followed a golden rule, namely, that whenever a published fact, a new observation or thought came across me, which was opposed to my general results, to make a memorandum of it without fail and at once; for I had found by experience that such facts and thoughts were far more apt to escape from the memory than favourable ones. Owing to this habit, very few objections were raised against my views which I had not at least noticed and attempted to answer.” - Charles Darwin (autobiography)

See also: Motivated skepticism, Privileging the hypothesis, Falsifiability, Heuristics and Biases, Availability heuristic, Surprise, Narrative fallacy

External Links

Speculations on the Future of Science by Kevin Kelly
On the Failure to Eliminate Hypotheses in a Conceptual Task by P.C. Wason
Write Your Hypothetical Apostasy by Nick Bostrom
Confirmation Bias, Wikipedia