Mental toughness, determination, willpower, perseverance ... whatever words you use, the ability to overcome roadblocks, to push through doubt and fear and hesitation and keep working hard to achieve long-term goals is what sets successful people apart.

So how can you develop greater mental toughness? The first step is to realize that you always -- always -- have more in you than you think. When you're doing something difficult and you think you need to stop, you don't. You have more in you. When you're trying to overcome a bad habit and you just don't think you can, you can. You have more in you.

When you're about to give up on yourself, because whatever you're trying to do just seems too hard, you shouldn't. You have more in you.

That's what Jesse Itzler learned when a SEAL moved into his house for a month. (The best-selling Living With a SEAL is based on that experience.)

The first day, the SEAL said, "How many pull-ups can you do?" Jesse, who says he's not great at pull-ups, managed eight pull-ups.

The SEAL said, "Take 30 seconds and do it again." This time, Jesse managed six. Thirty seconds later, he barely did three or four pull-ups, and, as he says, "I was done ... 'couldn't move my arms' done."

And the SEAL said, "All right. We're not leaving here until you do 100 more."

"I thought, 'We're going to be here for quite a long time,'" Jesse says, "because there was no way I was going to be able to do 100. But I ended up doing it one at a time ... and he proved to me right there that there is so much more we are all capable of than we think we are. It was a great lesson that we have so much more in our reserve tank than we think we do."

 

That one experience, repeated throughout the month in various ways, caused Jesse to decide:

He would say that when your mind is telling you you're done, you're really only 40 percent done. And he had a motto: "If it doesn't suck, we don't do it." And that was his way of every day forcing us to get uncomfortable to figure out what our baseline was and what our comfort level was and just turning it upside down.

We all have that will. It's just a matter of how we apply it not just to the once-a-year marathon, but to a variety of things in our daily lives.

Intuitively, you know he's right. Think of times when you had a reason to push past your self-imposed limits. Think of a time when fear, desperation, or even a huge incentive helped you push past what you would have seen as a barrier.

Determination is a muscle that grows stronger the more it is exercised.

Next time you think you've reached your limit, do one more. Next time you think you can't go on, go a little farther. Challenge yourself to see if you can endure just a little more.

In time, challenging yourself will become a habit -- and so will accomplishing much more than you would have ever thought possible.

After all, if a guy like me can do 5,000 push-ups in one day ... imagine what you can do if you try.