Birthday

Harry becomes his true self;

"suddenly a searing pain race through his spine into his head Harry collapsed to the ground in agony...

...his vision started to close in and fade to darkness and then all he knew was the shadows of his own eyelids."

Or

Harry realises that Dumbledore may not be all that he's made out as and really just a manipulative old man. This leaves him no choice but to take his destiny and future into his own hands... there's no telling what he could become.