It is very hard for me to switch from clay to grass.

One of the most important things, actually, when you're playing on grass, is to move.

I pass through the difficult moments in life, really difficult times on grass, during my seven years of my career. All of a sudden I felt comfortable.

You cannot change me; this is the way I am.

I've had good times and bad times. That's me. That's how I am.

Roger [Federer], he brought tennis... one level higher. Normally he toys with everybody. With all respect to other players, he does whatever he wants on the court against them. It's incredible what kind of game he can play.