Mind over matter.

Is the challenge you're taking on physically challenging or emotionally difficult? Even if it is, could it be that your obstacle is also mostly mental?

Jesse Itzler, the co-founder of Marquis Jet, talks about mental toughness in his book, Living with a SEAL. While running a 100-mile race as part of a six-person relay team, Itzler met a Navy SEAL who was running the entire race by himself. 

Running the race solo was a massive feat on its own--and then Itzler came to realize that the SEAL was running despite a damaging set of circumstances. Recalls Itzler,

I've never seen anything like it. And during the race, I kept an eye on him and around mile 70--he weighed probably 260 pounds, which is quite large for an ultra runner--he had broken all the small bones in both of his feet and had kidney damage and he finished the race.

After the race was over, Itzler hired the SEAL to live with him and his family in an effort to learn more about mental toughness. "I thought that he would be a great way to get in good shape," Itzler says, "but also to just mix up my routine and get better."

Who was the SEAL who came to live with Itzler? None other than Ironman triathlete David Goggins, world record holder for most pull-ups done in 24 hours and finisher of the Badwater 135, a 135-mile race in Death Valley (Goggins finished in fifth place). 

Not only did Goggins run the ultra-marathon with broken bones and while weighing over 200 pounds, but he did so while suffering from an endurance-limiting atrial septum defect caused by a hole in the wall of his heart. 

While Goggins was living with Itzler, he taught him the "40 percent rule": "When your mind is telling you you're done, you're really only 40 percent done." Itzler then explained how Goggins showed Itzler that he could actually do 100 pull-ups, despite nearly quitting after completing only eight.

Try living by the 40 percent rule in your own life, whether it's during exercise, in relationships, or in business. Challenge yourself to dig deeper, and to ignore the mental limits you place on yourself as you travel the road to success.

Pain is not something you want to avoid all the time, because when we continuously subject ourselves to it, we only grow stronger. As American runner and coach Joe Henderson once said,

Your toughness is made up of equal parts persistence and experience. You don't so much outrun your opponents as outlast and outsmart them, and the toughest opponent of all is the one inside your head.