In “Unbreakable” (2000), Bruce Willis played a middle-aged man who discovered that he was an invulnerable superhero.

Obviously, superhero movies require our suspension of disbelief.

In “Unbreakable,” the hardest thing to believe was not that Willis’s character was invulnerable, or that he had super strength. Those are standard in superhero movies.

The hardest thing to believe was that he had reached middle age without noticing that he had never been injured or sick.

On the other hand, I could believe it at least a little. My father was almost never sick.

No, the cause wasn’t regular exercise. It wasn’t a healthy diet. It wasn’t even good heredity. And he wasn’t a superhero.

It was because even if he was sick, he would almost never admit it.

And there’s a lesson in that.

The lesson is not that we should ignore illness. As a doctor, Dad would never have recommended that. He got away with it, but most people can’t.

The lesson is that a lot of what happens in our lives depends on our attitude toward it.

Dad meant to do his part for the world. If illness thought it could slow him down, he invited it to try. In the meantime, he was going to live, and live fully. He succeeded.

He also believed that he was lucky. He said you might beat him at a game of skill, but that he’d always win if it depended on luck.

I think there was a different cause.

Dad was lucky because he interpreted things that happened to him as lucky. He always looked for ways to make bad things work for the good. And then he felt grateful for being so lucky.

I think he was about as happy as a non-psychotic person can be. He was lucky that way.

We can be lucky that way, too — if we face life with courage and always look for ways to turn bad things into good.

It’s a smart way to live.