Denial is a psychological defense mechanism in which a person faced with a fact that is uncomfortable or painful to accept rejects it instead, insisting that it is not true despite what may be overwhelming evidence.
Unlike some other defense mechanisms postulated by psychoanalytic theory (for instance, repression), the general existence of denial is fairly easy to verify. However, denial is one of the most widely controversial defense mechanisms, since it can be so easily used to create unfalsifiable theories: anything which is said or done by the subject which does not fit in with the interpeter's theory of reality is explained, not as evidence that the interpreter's theory is wrong, but as the subject being "in denial".
A commonly used example of denial is if an authority came to the house of two parents whose child just died and informed them for the first time about this, and the parents said something such as "No! You must have the wrong house, you can't mean our child!"