Let me begin by telling you a story.
In the 2008 Summer Olympics, Michael Phelps was churning water in the pool. In one race however, he had a problem. There was moisture inside his goggles. By the third turn in the final lap his goggles were filled with water, and he couldn’t see a thing.
Here is how writer Charles Duhigg chronicled the incident:
The leaking goggles were a minor deviation, but one for which he was prepared. Bowman [Phelps’s coach] had once made Phelps swim in the Michigan pool in the dark, believing that he needed to be ready for any surprise. Some of the videotapes in Phelps’s mind had featured problems like this. He had mentally rehearsed how he would respond to goggle failure. As he started his last lap, Phelps estimated how many strokes a final push would require—nineteen or twenty, maybe twenty-one—and started counting. He felt totally relaxed as he swam at full strength.