Cognitive therapy has been around for a while - since the 1960s, in fact - and has found several different applications in modern psycho-therapy, including being used as a treatment option for depression. A person can be described as suffering from depression when their negative feelings and thoughts are, to them, overwhelming and affect all aspects of their life. Depressed people are usually extremely dysfunctional, as they see everything that happens to them through the negative filter of their depression, and this is why cognitive therapy, which tries to change dysfunctional behavior, can be so successful in the treatment of depression. Cognitive therapy seeks to change how a person copes with negative and stressful events by changing how they feel and what they think about these events. A person who suffers from depression will, for instance, be negatively affected by certain events in their life - personal rejection, for instance - and their depression will magnify the importance of the event out of all proportion. If, however, that person is undergoing cognitive therapy, their therapist will attempt to change how they view and interpret the event in order to change how they react to it and to decrease the importance they place upon it. The theory behind cognitive therapy states that adults who become depressed had usually developed the potential to do so in their teens due to various negative events that happened to them while they were growing up. These negative events needn't be overwhelmingly traumatic, however, and can include such relatively common experiences as being bullied at school or losing a parent or close friend. The theory goes on to state that these people usually feel depressed and negative about three major aspects of their life: their future, their self and their environment, and that they will increase the negative significance of any event that happens to them unless they are taught how to change the way they perceive and react to these events. Cognitive therapy encourages depressed people to change the way they think, react and feel by making small and manageable changes every day, and it's this gradual change of perception that seems to work best.