Psychological numbness is a mental self-defense mechanism used to prevent psychological trauma, in which a mental entity chooses to ignore thoughts or emotions relating to a specific body of knowledge, emotions, or ideas. This is often induced by social conditioning. Psychological numbness is an important component of sanity in an individual whose basic moral principles or ideology would be rendered inapplicable by comprehending the full implications of an action or occurrence.

A well-recognized situation of psychological numbing is that associated with killing another person. By being numb, the person refuses to recognize the implications of having killed the person, allowing their psyche, as it existed before, to continue as it was. If the person did not numb themself, psychologically, the person would go into shock, that they have caused another thinking, feeling entity to cease existing, then moving on to stages of self-loathing, recognizing oneself as the other- a murderer- and then to further stages of dealing with trauma, such as denial, 'bargaining', and, eventually, acceptance.