Imam Khomeini explains the matter through his famous book "Combat with the self" as following:
If you thought a bit about the affairs of the other world and its terrible path you would give more importance to the heavy duties and responsibilities which rest upon your shoulders.
There is also another world for you, there is also the resurrection. (You are not like other existents for which there is no returning.) Why do you not take warning? Why are you not awake and conscious? Why do you so heedlessly engage in backbiting and speaking ill of your Muslim brothers, or listening to such things? Do you not know that the tongue which wags in backbiting will be trampled under the feet of others on the day of resurrection?
Have you heard that backbiting will be food for the dogs of hell? Have you never given a thought to how evil are the consequences of these differences, enmities, jealousies, cynicism and selfishness, and arrogance and conceit? Do you know that repercussion of these wicked forbidden deeds is hell and that it is possible, God forbid, that they will lead to the everlasting fire?
God does not want man to be afflicted with illnesses unaccompanied by pain, for when an illness is accompanied by pain, it forces man to seek a cure, to consult a doctor or go to hospital, but an unfelt illness without pain is more dangerous. By the time one becomes aware of it, it is too late.
If mental illnesses were accompanied by pain, this would be something for which to be thankful. Ultimately, man would be forced to find a cure or a remedy.
Read more:
Imam Khomeini warned against becoming aggressive during academic discussions