It is very important tackle this behaviour immediately before it turns into an addictive habit. The best way is to help your son believe in himself. " TOTALLY STOP CRITICISM FOR THE TIME BEING" Give him to perform tasks that are easy and you know he can perform well. Start giving him points for that and a small momento or gift. Keep on appreciating every little effort he puts in. Let him take the baby steps. Make him look into the mirror make eye contact with self in the mirror and say the following affirmation each morning I Can do anything and everything I believe in myself I am good at many things Also keep on saying and showing through actions that you believe in him