oh sorry, I didn't mean to take anything away from nadal, but I think even nadal fans will agree that fed does have some sort of mental block when he faces nadal.
I'd argue that that's something that builds up over time with someone whose game you can't seem to get around.
I was watching a clip the other evening of them in RG 2005, and you could tell that Roger was getting more and more frustrated because no matter what he threw at Rafa, Rafa got it back to him, and you could tell how unused to that Roger was -- with those crazy angles of his, he's accustomed to putting shots where his opponents can't get to them, especially back then when practically no one else could ever beat him.
So, yes. If you're still dealing with that four years later - because you're not willing to adjust your own game, because it still beats pretty much everyone else,
and also because the other player keeps improving
his game - if you're not Rafa, with some zen way of only focusing on the point/game/match in front of you, any reasonable player would build up some sort of mental block against that kind of opposition over time, I'd think.