I carry my board up the beach. "I could never do that," a man walking by yells. "I'd be too scared."

"Sure, you could," I think as he walks away. Paddleboarding is hard but not that hard. First you fall off. Then you fall off some more. But soon you get better. And what's to be afraid of? You get wet and climb back on. Except for some occasional embarrassment, the downside is no greater than that of jumping in a swimming pool.

Very soon paddleboarding is relatively easy--and if it's easy for a nonathletic guy like me, it can be easy for anyone. You just have to be wiling to try.

I walk offstage after speaking to 4,500 people. A sound tech shakes his head. "I could never do that," he says.

"Sure, you could," I think. It's hard, but not that hard. First you struggle because you haven't figured out what you want to say doesn't matter--all that matters is what your audience will benefit from hearing. Then you work and revise and find your hook and your story. And you practice. And what's to be afraid of? That you'll fail? Sometimes we bomb when we speak to one person; the only difference is the degree.

In time, speaking is relatively easy--and if it's relatively easy for someone as shy and insecure as I am, it can be fairly easy for anyone. You just have to be willing to try.

I climb, stiff-legged and sore, off my bike after riding nearly 100 mountain miles to complete the inaugural Alpine Loop Gran Fondo. I gratefully accept a bottle of water from a volunteer. "That's impressive," he says. "I could never do that."

"Sure, you could," I think. Sure, it's hard, but it's also just a question of putting in the miles. First you ride 3 miles. Then 5, then 10. Then you work up to 25-mile rides. Then 50. Then you throw in the occasional longer ride.

And months of training later, you can finish a Gran Fondo that goes over four mountains--even if you're a bird-legged old man who initially possessed the speed, power, and cardiovascular fitness of a possum.

Life throws up enough barriers. Genetics. Education. Intelligence. Athletic ability. The list of reasons we can't do certain things is endless. No matter how hard I work I'll never be as talented as LeBron James. Or Usain Bolt. Or Maria Sharapova. Or Stephen King or Stephen Hawking or Stephen Colbert.

They're all bigger, stronger, faster, smarter, more creative, or much, much funnier. Those are barriers I could forever work to overcome but likely never surmount. I can go far…but probably not that far. (If you haven't gotten the point yet, I am definitely nothing special. If I can do interesting or challenging things--imagine what you can do.)

But then there are the hundreds of barriers we construct all on our own without any justification. We don't know we can't; we just decide we can't. So we decide we shouldn't.

We decide whatever we might want to do is too hard, too challenging, or too scary for a person like us.

And that's why five of the saddest words you can say are, "I could never do that."

Because, in almost every case, you can. Maybe not to a world-class level, but definitely to a superior level. The only real difference between the people like us and people doing the things we would like to do is that they didn't reflexively choose to put up their own barriers. They didn't automatically decide they can't.

Instead they just decided to try…and then to keep trying.

Granted you may never become Steve Jobs. Or Mark Cuban or Richard Branson or Sara Blakely. The barriers to reaching their level of success may be too high.

But you can still be a better you than you currently believe possible. You can still achieve amazing things…and average things…and silly, frivolous little things that have meaning only to you. All you have to do is decide to try.

When you do, you'll soon find you no longer put up barriers to any of the things you "can't" do.

You'll be too busy enjoying all the things it turns out you can do and dreaming up more things to accomplish--and enjoy.