High school seniors dominated the program I attended the other day, their chests involuntarily puffed up, their smiles and strides unconsciously confident.

I can think of only one way to describe the look, the feeling, the demeanor of graduating seniors: bulletproof.

We’ve all had that feeling, not for long perhaps, but we’ve had it. It can happen anytime, coming and going just as quickly, and for most of us, the first time it happened was high school graduation.

That day is still burned into my memory, tossing mortar boards into the air just like on TV, graduating with honors and heading off to myriad parties and celebrations. I was pumped full of myself, bulletproof; but then, so were we all.

As the summer wore on, many of my fellow graduates and I had few responsibilities, few ongoing entanglements, just expectations of greatness and great expectations of life.

And then as my friends began leaving for college, slowly but surely, I was the last one left in town. When the day arrived to head out of town for good, I slid into my car seat, hugging my crying mother and taut-faced dad for the last time. As I turned the car down the driveway, I looked back but couldn’t see them, tears streaking my cheeks and dousing my vision, the feeling of being bulletproof giving way to the feeling of having taken a mortal wound.

For me, the first few college years were tough and lonely, and the feeling of invincibility never did come around there, not that I ever stopped trying to get it back. It was years before I felt bulletproof again. When I turned 30, for just a moment I had it all: good job, new home, lovely bride-to-be. Then in a flash, I had cancer and at the same time found the FBI and Justice Department sitting in my living room, questioning me about my employers. In a matter of days, I went from bulletproof to shell-shocked. That’s how it goes, isn’t it?

Everything worked out, but it took 15 years of hard work before I again felt bulletproof, and then it was another cancer diagnosis that knocked me down. It took most of the next year to find out the diagnosis was wrong, but maybe the mental turmoil of that time will keep me from ever feeling bulletproof again.

Then again, maybe not.

Today’s high school seniors will learn, as we’ve all learned, that being bulletproof isn’t a permanent state of mind. And that’s a good thing, because without knowing what it’s like at the peak, there would be no joy in making the climb every other day. They’ll learn that soon enough, too.