1. An often unreasonable idea that may or may not have been true at one time and has become fixed, immovable and inaccurate despite evidence to the contrary or efforts to ignore it; an obsession. Usually, the person refuses to examine or dismantle these ideas. Some examples are: “I’m too old.” “I’m too young.” “Children should be seen and not heard.” “I cannot trust anyone.” “I’d better do it myself.” “I can’t do that.” 2. Something accepted without personal inspection or agreement.