I have a Ph.D. in philosophy and sports science. At 14, I went through this really tough Soviet training system. A lot of my roommates got psychologically broken or physically injured. Either you came through, or you were out. I made my Ph.D. work in the field of young athletes aged 14-19 because at this age any human is changing.

Obsession is love in an extreme shape.

I'm playing right now a role, and the role is called the 'Heavyweight Champion of the World.' And it takes all of the time. And I love this role, and it takes a lot of attention for me for the sport, and I just don't want to lose the title, so that's why I have to stay focused and not become an actor.

I would say that Roger Federer is pretty amazing. And Manny Pacquiao - he's such a tiny, little lightweight guy, but the way he fights makes people so excited.

When you're successful for so many years, the scariest part is that you're getting too comfortable because you've had so much success.

I should say that mental strength is No. 1, experience [is] No. 2, physical strength is No. 3, and genetic ability that you're getting from Mother Nature probably comes after.

You have to learn the opponent psychologically inside out and mental strength is one of the important makers. You're either gonna break it or make it.