Defenses like projection, reaction formation, and displacement, were first identified by Sigmund Freud.  What exactly are these defenses, though? How do we use them to deal with threatening feelings and difficult thoughts? 

Defenses are complex psychological maneuvers or mental gymnastics that individuals employ—usually out of conscious awareness—to control the direction of the mind or to try to block what feel like unacceptable thoughts, feelings, or impulses.

In plain English: say your friend forgets your birthday. She does it every single year.  You feel hurt, even angry, but are uncomfortable accepting that the anger is your own (perhaps the message you received growing up was that it isn’t nice to find fault with people, or that anger ruins relationships).  Your mind disavows the anger; instead, in a complex mental maneuver, your mind unwittingly experiences the anger as coming from outside of you.