Prayer at its best is the expression of the total life for all things else being equal our prayers are only as powerful as our lives

Selfishness is never so exquisitely selfish as when it is on its knees. ... Self turns what would otherwise be a pure and powerful prayer into a weak and ineffective one.

God may allow His servant to succeed when He has disciplined him to a point where he does not need to succeed to be happy. The man who is elated by success and is cast down by failure is still a carnal man. At best his fruit will have a worm in it.