Originally Posted by Seventh Path
When a memory gets repressed... it tends to repress many things about it. The brain doesn't differentiate the difference between a "good" memory and a "bad" memory. It just knows trauma happened and closes off anything associated with the trauma.
The thing that got repressed was seeing Itachi cry. It didn't get repressed because it was bad. His mind could NOT comprehend it. His brother basically showed him he was a soulless murderer. Why would he cry? His young mind couldn't set the thought in his head so it got wiped. Unlocking the sharingan consequently got wiped along with that particular memory.
When the mind is cutting away at memories it's not precise. In fact, it is quite crude and tears away things you may have wanted. Therefore it is not only possible, but probable that this could happen.
The thing is though, if that memory of itachi crying actually got repressed, then he wouldn't be able to remember what happened the night his family was killed either. Your brain locks away traumatic events above all else in order to protect you. Yes, he said it didn't make sense, but it is equally true that it made even less sense for itachi to kill his entire clan (in sasuke's eyes anyhow).
Also, unlocking the sharingan happened before sasuke saw itachi cried, so you can't say "he remembers his parents dying because it's a separate memory". So is awakening the sharingnan.
If his brain was locking away what it didn't understand, then he wouldn't be able to recall the details of that night as far as going into the room and seeing his parents dead, etc.
That is obviously not the case, therefore, his brain did not lock away memories that he didn't understand based simply on the idea that he didn't understand them.