Arguably the greatest runner in history is an Ethiopian man named Haile Gebrselassie. He broke nearly 30 world records in a career that spanned from the early 1990s through 2015. He has won eight World Championships gold medals, two Olympic gold medals, and numerous major marathons. Now at least 38 years old (it is widely believed he is actually three or four years older), Gebrselassie remains among the fastest distance runners in the world.

In the early part of his career, Haile Gebrselassie was believed to be dominant simply because he had more natural talent than other runners. But the longer his reign of dominance has extended, the more apparent it has become that Geb’s success has as much to do with his mental attitude as with whatever genetic advantages he may have.

Gebrselassie set his first marathon world record in Berlin in 2007. After crossing the finish line he was swarmed by reporters. The first words they heard him utter were these: “I can run faster.” The following year Geb returned to Berlin and set another world record, bettering his own mark by 27 seconds. He immediately set about trying to run even faster.

Haile Gebrselassie is the greatest runner who ever lived not only because he is extremely talented but also because he is never satisfied. This is a hallmark characteristic of champions in every sport and of successful people outside of sports as well. Mediocre performers in sports and beyond pat themselves on the back when they achieve goals. Champions don’t. Not even one minute after doing better than they ever have before (perhaps even better than any human being has ever done before) they decide that they could have done better—and will do better.

People who don’t have this mindset often assume that an athlete who is never satisfied is an athlete who never allows himself to enjoy his sport. This is not true. You can have a never-satisfied mentality and simultaneously maintain a great passion for your sport or entrepreneurship or whatever else. In fact, Haile Gebrselassie is beloved by runners around the world because he never stops smiling and because his passion for running is always so evident. His inability to ever be content with anything he achieves does not get in the way of his passion for running—it is an expression of his passion. He has an insatiable hunger to reach higher. He loves trying to reach higher, whether he succeeds or fails.

No matter what your passion is, you will get both more success and more enjoyment from it if you are never satisfied.