A manager must know his people and adjust his approach accordingly. Suit your control to the individual. Failure to keep communication lines open. Delegation can only flourish in a climate that encourages communication between the boss and his people. Being too narrow in your delegation.
Delegation is a form of training.
So don't restrict yourself to delegating the kinds of things employees know how to do best. Try them out on tasks for which you suspect they may have some aptitude but have had no opportunity to exercise. You may strike gold. Worry is a great common denominator. As long as there is uncertainty in the world, we'll worry.