Some feel that anyone with serious issues with depression can be cured if the depressed person would just start thinking positively. It would be nice if it were that simple. But it isn't. Don't get me wrong-positive thinking can be quite powerful. However, a person with clinical depression, especially severe depression, is less likely to believe in much of anything positive. So while positive thinking can help at times, it's not going to always work. If a person tries to think positive, it's not necessarily going to work if the person can't get himself to actually believe in the positive statements he's making to himself.
