Tennis Quote of the Day: What Separates the World's Top 4 Men Players from the Rest?

Question: What Separates the World's Top 4 Men Players from the Rest?

Answer: "It's mental strength . . . to [consistently] hit the right shot at the right time."

Novak Djokovic, in his post-match interview with Jim Courier after his Round of 16 victory at the Australian Open 2012