How do defense mechanisms contribute to psychopathology?

Defense mechanisms were an idea first put forth by Freud. They are ways of taking care of stress or bad situations that he claimed use up some mental (ego) strength. When all of this ego strength is used up, there is no more room for new defenses. This means that if you encounter a bad situation and need to use a defense mechanism you will probably revert to an earlier time or have some mental harm other than that because you are trying to find ego strength.More recently, people have claimed that these defense mechanisms can cause a person to live in "their own little world" that is different from ours. When forced to live in our world, that causes some distress to the individual and their behavior may seem abnormal to us (although it is normal in "their" world).