Sigmund Freud first coined the term "defence mechanism" to describe unconscious coping strategies the mind uses to reduce anxiety from unacceptable thoughts, feelings, or external threats. Defence mechanisms can be helpful in small amounts but become maladaptive if overused. Common defence mechanisms include repression, denial, rationalization, and projection. The purpose of defence mechanisms is to protect the ego and reduce anxiety, though they can distort reality if taken to an extreme.