In our busy lives, we have developed behaviors that prevent us from dealing with situations in a healthy manner. These behaviors are defense mechanisms to help us cope with thoughts, feelings, impulses and emotions.
I have noted a few below from the teaching of Sigmund Freud:
Repression is an unconscious mechanism used to keep disturbing or threatening thoughts from becoming conscious. This is not a very successful defense in the long term since it involves forcing disturbing wishes, ideas or memories into the unconscious, where, although hidden, they will create anxiety.
Projection involves individuals attributing their own thoughts, feeling and motives to another person. For instance, you might hate someone, but you try to 'solve' the problem by believing that they hate you.
Displacement is the redirection of an impulse (usually aggression) onto a powerless substitute target. The target can be a person or an object that can serve as a symbolic substitute. Someone who is frustrated by his or her supervisor/boss may go home and kick the dog or beat up a family member.
Sublimation is similar to displacement, but takes place when we manage to displace our emotions into a constructive rather than destructive activity. This might for example be artistic. Many great artists and musicians have had unhappy lives and have used the medium of art of music to express themselves. Sport is another example of putting our emotions (e.g. aggression) into something constructive.
Denial involves blocking external events from awareness. If some situation is just too much to handle, the person just refuses to experience it. For example, addicts may refuse to admit to themselves that their addiction to drugs (ilicit, prescribed, or alcohol) is bad for their health and is causing him or her legal problems.
Rationalization is the cognitive distortion of "the facts" to make an event or an impulse less threatening. We do it often enough on a fairly conscious level when we provide ourselves with excuses. In other words, many people are quite prepared to believe their lies.