Board Thread:Naruto Discussions/@comment-18016240-20160208110013/@comment-734582-20160417114945

It's not said directly, but heavily implied that the Sharingan gives eidetic if not photographic memory.

It's not that the Uchiha are mentally unstable. To them, every moment of happyness can be recounted as if it were the first time. And when they experience great loss, they can experience that loss as vividly as the first time, even if it were the thousandth. To them, pain doesn't fade like in a normal human.

When Sasuke achieved EMS, it's heavily implied that he saw everything Itachi saw. The Sharingan's excellent vision also curses the Uchiha.