Revenge was less understandable... less... him. Harry knew he had a temper, but he’d always found it easy to forgive and forget. What was the point of carrying grudges? First had been the Durselys- the constant abuse - what right did Harry have -the poor unwanted relation - to begrudge their treatment? Then as he grew up in Hogwarts, he learned his real background, how his parents had died for him, and that Voldemort was after him. What use would it have been focusing on the wrongs done to him when he would die soon, anyway?