A lot of people change for good. Some people just fall off. Just trying to progress in anything, no matter what you're doing, I feel like any progression you make... some people aren't gonna be around you that were around you.
You have to have the service mentality in the sense that you subjugate your own ego, and you subjugate a large part of your own life to really helping other people, being successful on their behalf.
I admire a lot of people, but in terms of sport I've always loved the mentality of Tiger Woods on a golf course. I always love his eyes when he's setting himself and focusing on his decision; he has a really strong, focused face and believes that he can make the shot.
Certainly I would like to have some of the qualities of other players and obviously from Roger Federer. But believe me, there are plenty of other abilities that are important, particularly mindset and strength.
In your career you have a lot of good moments and bad ones. The important thing is to have enough motivation to keep working all the days with humility and trying to be a better player than before. I am going to try to continue doing this.