I'm sure this was said before. I think it's a simple formula. If you play hard physical game, it will catch up with you relatively sooner than later. You will simply burn out or injuries will start creeping up. Rafa is no exception. Like someone said, he is trying to match Federer's slam record but with his style of play I don't think he has a chance and I haven't even mentioned mental part.
Yes you have a point. Something Rafa said about Djoko starting the ascent of his great performances at the wrong time made me think . Was he really thinking of his own rise to the top and all the pain and hard work he has had to endure and was he thinking that Djoko will have a short time span? It is hard to look into what is going to happen this year and it will be crucial but not really the end of Rafa's rise to being number one. It all depends on whether Djoko can keep it up and nobody knows better than Nadal what a price Djoko will have to pay to continue his rise