The human body and brain work in very complex ways and  science still does not exactly know how depression works and how it can be successfully treated in every circumstance. Some anti depressive medication will work for around 60% of people experiencing primary depression but we still do not know why it will work for one patient and not for another. Depression is not just something that will happen to you when a bad thing occurs to you, there is a complex sum of factors that will decide if someone will become depressive.

There are different theories about how a depression develops in a person and the most prominent one is the threshold theory. It basically states that in theory everybody could develop a depression but the sensitivity differs from person to person. This sensitivity is often inherited genetically from their parents/family. You could picture this by drawing a line from 0 to 100 where zero means that you are not likely to develop a depression soon while 100 means that you are on the edge of a depression episode. Some people will start at zero while others will already start on 50 or 60 or every other number.

You will go up in sensitivity when you are going through very difficult phases like death from a loved one, teased at high school, rape, etc. With every life event that you pass there will be an increased possibility on a depression. This theory is called the life event theory.

You have to understand that this is a very basic method to explain how it could work and that we still do not know exactly how someone will develop a primary depression or manic depressive disorder. However, research does state that one person will develop a depression much faster than someone else and although some of it can be explained by these two theories, they can not fully understand why some people will develop a depression and why others don’t.