Many people do not understand the nature of depression. Even some medical doctors do not understand depression. Depression can be caused by several factors. You can have depression because of a major trauma (associated to PTSD) or for a sudden change in your environment. But also you can have depression while you do not have traumas to overcome. Depression itself is a "real problem" and it is epidemic.
Successful people can have depression Forbes Welcome
Also you can see https://en.m.wikipedia.org/wiki/List...ssive_disorder