In Journey’s End, Ten tries to save Davros, and gets mad at Tentoo for destroying the Daleks. In The Day of the Doctor, he cheers gleefully at their destruction. In The End of Time, Ten is horrified at the Time Lords returning, and fiercely willing to do whatever it takes to send them back to hell. In The Day of the Doctor, he’s so happy to save them he’s grinning ecstatically, and jumping around with joy. In The Day of the Doctor, Ten is so blatantly out of character, sometimes I really believe he was a Zygon copy. And the Zygon and the Moment were working for Rassilon to trick the War Doctor into saving Gallifrey, as they were Rassilon’s B-plan all along. And thanks to Eleven, the plan worked.
Headcannon accepted. His characterization in the Day of the Doctor pissed me off so much!