I feel I owe you another explanation Harry," said Dumbledore hesitantly. "You may, perhaps, wondered why I never chose you as a prefect? I must confess...that I rather thought...you had enough responsibility to be going on with."Harry looked up at him and saw a tear trickling down Dumbledore's face into his long silver beard.
J.K. Rowling, Harry Potter and the Order of the Phoenix
dumbledore, harry-potter, prefect, responsibility