Nobody is even close to Rafa's mental strengh, i've said this many times, i honestly believe that in the top 20 there're lot of players with better tennis skills than Rafa but that's all, Rafa is superb, he's been improving his game since day 1.
He's able to adapt his game to each tournament( Fed can also do that btw), he gives a shit about serving super well when he plays on clay for example, but knows it's important and focus on serving well when he plays on hard, about grass well in my opinion it's the best surface for him, better than clay, his game is even more spectacular.
The only guy close to Nadal's mental strengh is Gulbis..........................................

Never underestimate the pain of a person, because in all honesty, everyone is struggling. Some people are just better at hiding it than others.