Sri Chinmoy: Insanity is an imperfection in our nature. It is a result of our inner imperfection. In our outer life we have no need for Light. We have need for everything else but we are afraid of Light. When we think of Light, instead of feeling that we will be illumined we feel that we will be exposed, and we try to hide ourselves.
Insanity can start in any plane of consciousness, but when it develops in the mental plane we notice it. Before it develops in the mental plane it can develop in the inner plane, the psychic plane. When insanity starts it does not start all at once in the physical. It descends like rain, as a downward flow into our system. And only when it enters and captures the mind do we lose our mental balance. Insanity starts when we do not keep everything in our mind in the proper place. Thoughts, inner actions, inner ideas, ideals, facts — everything has a place of its own in the mind. When we misplace these things or when we do not give them their proper importance, then we develop insanity.