Strict Adherence to Perfectionism
People who believe that there exists a perfect way or a formula to complete a certain task, and anything less than that perfect way is tantamount to failure, fail more often than succeed. These people tend to see failure as a hurdle, rather than seeing it as a building block towards success.
Feeling Unworthy of the Good Things in Life
People who believe that they got that special promotion or their desired job as a fluke, rather than due to their potential, often are of the belief that they don't deserve the good things in life. This may stem from an inferiority complex, or a low self-esteem, that remain unattended from an early age, and could not be diagnosed.
Seeing Problems Instead of Possibilities
There is a story in which a rich father gifts his pessimist son a valuable watch, to which the son becomes gloomy, and says, "the watch will require changing of the batteries to keep it running". On the other hand, when he gives his optimistic son a room full of horse dung, he sees him digging through the manure using a shovel. Out of curiosity, the father asks him what he is doing! The son replies, "since there is so much horse manure, there's gotta be a horse in there somewhere.