Doubt is that state of mind where it's is not fully alive. Answers cannot satisfy doubt. Hearing and seeing cannot eliminate doubt. Only prana can eliminate doubt. When doubt arises in your mind know that prana has gone down. The life in you is dull. The wick in the lamp is going down. On the day you do pranayama and Sudarshan Kriya, you are so alive. Every cell in your body is alive and then there is no doubt in the mind. +Sri Sri Ravi Shankar