Rationalization

In psychology, rationalization is the process of constructing a logical justification for a decision, action or lack thereof that was originally arrived at through a different mental process.

This process can be in a range from fully conscious (e.g. to present an external defense against ridicule from others) to mostly subconscious (e.g. to create a block against internal feelings of guilt).

For an example, consider a person who bought one of the first home computers in 1980 primarily motivated by the excitement of playing with a computer. If he felt that his friends would not accept "having fun" as a sufficient reason for the purchase, he might have searched for other justifications and ended up telling them how much time it was going to save him in doing his taxes.

Rationalization is one of the defense mechanisms proposed by Sigmund Freud, which were later developed further by his daughter Anna Freud.