http://en.wikipedia.org/wiki/Rationalization_%28making_excuses%2

In psychology and logic, rationalization or rationalisation (also known as making excuses[1]) is a defense mechanism in which controversial behaviors or feelings are justified and explained in a seemingly rational or logical manner to avoid the true explanation, and are made consciously tolerable – or even admirable and superior – by plausible means.[2] It is also an informal fallacy of reasoning.[3]

Rationalization encourages irrational or unacceptable behavior, motives, or feelings and often involves ad hoc hypothesizing. This process ranges from fully conscious (e.g. to present an external defense against ridicule from others) to mostly unconscious (e.g. to create a block against internal feelings of guilt). People rationalize for various reasons — sometimes when we think we know ourselves better than we do. Rationalization may differentiate the original deterministic explanation of the behavior or feeling in question.[4][5]