User blog comment:ImperiexSeed/Castiel's shifting of Sam's mental problems made no sense!/@comment-4807493-20120405133033/@comment-3481504-20120405195908

-Gives around of applause- Well obviously. Actually, it's all because of the damage done to Sam's soul.

Remember though, Michael tortured it too, although Lucifer more, probably cause of his unexpected defeat.

It could never heal, that's why Death put up the 'wall', in other words, it's incurable.