Roger Federer, the great tennis champion, has been playing tennis for 30 years, since he was four years old.

In a practice session before the US Open, he was tired. Federer wanted, as Michael Terry tells the story, to cut practice short. ”That’s when I started to run in and hit returns,” he said later. “I hit a couple for a winner. They were, like, ridiculous.” He tried it again in the next two practice sessions, to see if it actually would work again. And it did. So he tried using it in a match, and it worked again. A reporter suggested that he couldn’t get away with it against a top player like Novak Djokovic or Andy Murray. Federer laughed. “Why not?”

Hitting that new return made him think. Perhaps, he said, there are “so many things I actually can do that maybe I didn’t always know I could do or didn’t dare to do because I thought it was too crazy or — let’s say, the percentages weren’t, I wouldn’t think they would be in my favor. After this week I might look at that a little bit different.”

This blew my mind a little. Here was one of the greatest tennis players of all time acknowledging that he’s still discovering beliefs that are limiting his game.

Then again, one of the pitfalls of achieving success, in any arena, is being afraid to switch things up once you’re there. I’ve noticed, for example, that start-up entrepreneurs are focused on what they want to build and are open to trying anything. Established entrepreneurs, who have been running their business for years, however, are more concerned with what they stand to lose rather than what they might gain: Why change what’s working?

That’s where too much knowing can get in our way — we accept our beliefs as facts, the current reality as the extent of what’s possible.

So, how about this: Forget what you know for a moment and play the ‘what if’ game.What’s something you haven’t tried because you’re not sure if it would work or you think it’s ‘too crazy’?

Do you think the company would fall apart if you took a real vacation? That employees would take advantage if you offered them unlimited vacation, created transparency around salaries? That your team would make fun of you if you tried being more vulnerable/open/empathetic?

Now, after you hear yourself say, “No way, that’s too crazy,” ask: “Okay, but what if I didn’t think that?”

It takes imagination — to look at things differently, and courage — to feel uncomfortable and exposed. See what happens when you do it anyway.