GURPS uses "mental disadvantages" to model the personality of character ("good" and "evil" personality traits are disadvantages because they limit or impose behaviour). Mental disadvantages include ordinary personality traits ("honest", "curious", "shy", "bad temper"), phobias ("scotophobia", "triskaidekaphobia"), mental illnesses ("delusions", "hallucinations", "manic depression"), and various self- or externally-imposed behaviours ("vow", "code of honor", "addiction"). Characters gain extra points by taking disadvantages, allowing them to buy more advantages and skills. However, only the extremes of behavior are defined as strong disadvantages, while normal predilections and preferences are referred to as "quirks". Also, if a personality trait or physical trait would normally be defined as a "disadvantage" is created for a character in a game of GURPS where it would actually be an advantage, it's termed an advantage instead—and costs points.
Read more about this topic: Alignment (role-playing Games)