From Scientific American:

Many psychological studies show that on average, each of us believes we are above average compared with others—more ethical and capable, better drivers, better judges of character, and more attractive. Our weaknesses are, of course, irrelevant.

Such self distortion protects our egos from harm, even when nothing could be further from the truth. Our brains are the trusted advisers we should never trust. This "distorting prism" of self-knowledge is what Cordelia Fine, a psychologist at the Australian National University, calls our "vain brain."

Fine documents the lengths to which a human brain will go to bias perceptions in the perceiver's favor. When explaining to ourselves and others why something has gone well or badly, we attribute success to our own qualities, while shedding responsibility for failure.