Tennis has given me so many opportunities, and I feel very lucky to have achieved whatever I have, especially coming from a country that does not have a great history in the game.

Coaches were all saying that I was really talented and I had potential, but coming from Serbia, it wasn't easy. The '90s were the hardest years for our country - we went through two wars.

I think it's better not to mix professional life and personal life - although it is hard.

You want a coach who is going to push you and be strong and be in your corner when it's tough, but sometimes you have coaches who think they are more important than the players. That's where the conflicts come.

As I've moved along - not only my life, but my career and things like that - you look at yourself and start going, 'Oh, man, are you still doing what you set out to do? Are the ideals you had still the same?' Sometimes you measure up and sometimes you don't.

If I'm an entrepreneur, and I have a term sheet from Sequoia and Kleiner, that's the safe choice. Google Ventures is the brave choice.

Half of this business is politics. As real estate developers, it's our job to go in there and get beat up.

To a theoretical physicist, there is no greater joy than to see that this curious activity we call calculation - the depositing of ink on paper, followed by throwing away the paper and depositing new ink on more paper - can actually tell us something about reality.