hamlets flaw is often said to be procrastination, wich is another way of saying indecision, he hesitates and questions himself, his actions.. so "indecisiveness" is your answer.
Hamlet had several opportunities to avenge his father’s death by killing Claudius, but he lost out on them because of his indecisiveness. If he had killed Claudius at an early opportunity, Claudius would not have been able to carry out his scheme to have Laertes kill Hamlet in a duel.
