We are missing the solution because we don't understand the problem.

If I break my leg the cure is obvious: don't do anything for a month. Conveniently, it will hurt when I move my leg, so I won't try to move. The cure is only obvious because what actually constitutes the ailment (a broken leg) is obvious.

Now transfer this to psychological disorders. We don't know what exactly is wrong. Imagine if that were the case with the person with the broken leg. Current practice would be that the person goes to a doctor complaining that he doesn't feel like moving (because his leg hurts). The patient doesn't understand why, the doctor prescribes pain killers and - lo and behold - the patient feels like moving again. It worked! Great. But as soon as the patient tries to get off the medication, he finds that the pain returns (because the root cause of his symptoms has not been solved at all, he's probably worse off than he was before). In this example the so-called disease (leg pain, lack of willingness to be active) is not a disease at all. It is actually a part of the solution to the disease.

We are trying to 'cure' a disease without knowing what it is. When we try to solve problems without understanding their cause, we are bound to fail.

Human beings have accumulated enormous amounts of pent up emotion, that we began accumulating when thought activity started to appear in us hundreds of thousands of years ago. Before thought, emotion was solely the body's response to its physical environment, or more precisely: the body's response to its five senses. The body's natural response to emotion - fear, anger - is action which seeks to eliminate the threat: escape, fight (respectively).
When thought activity starts creating emotions, this approach no longer works. The mind can neither be escaped from, nor can we fight it. Well, we can fight it with alcohol, which many people resort to, but this is obviously not a real solution.

We have been trying to escape all these emotions that have pent up over the many many generations that have passed since thought first appeared in us, but are still stumbling because we don't understand what is happening. In some people emotions simply break out because it needs to. The body can simply no longer hold back the massive amount of emotional energy that has amassed in us since the birth of thought. Many people become insane when this happens; they are simply not able to handle the power of the emotions being released. Some jump off a building, others turn to drugs and alcohol, and yet others discover what is actually happening. They find out that there is nothing wrong with them, what is happening is actually quite healthy. They discover that they don't need to do anything; they are not sick. The symptoms that might be perceived as a disease (the massive out-flux of emotion) is actually the cure.

Resisting this process is what causes insanity. Emotional energy held back energizes the mind instead (it can't be held back) and the hyperactive mind creates more emotion, thus creating a vicious cycle that ends in either death, self-medication or a realization of what is happening. There is nothing wrong with anger, sadness or fear.
Treating emotions as a disease is the actual disease.