I’ve made a lot of mistakes. Big ones, little ones, expensive ones, incredibly expensive ones. Name it, and I’ve probably messed it up.

I’m OK with that. If you aren’t screwing up, at least occasionally, you aren’t trying hard enough.

Yet one decision I made–in response to a situation all of us often face–still haunts me.

In 2000 I took a management position at a commercial print facility that had just been acquired by a venture capital firm. Initially, I was put in charge of quality–ironic, since I came from a culture where productivity was everything, quality a necessary evil.

Every other member of the leadership team was also new. Randy was in charge of customer service and scheduling. We had worked together previously (and, in fact, he basically got me the job.)

John, the bindery manager, had more than 30 years of experience with R.R. Donnelley and Quebecor, two giants of the printing industry. Unfortunately that background didn’t serve him particularly well in his new role: His command and control leadership style fell totally flat with employees accustomed to playing the political games of a family-owned business.

Within a few months, I was put in charge of the bindery, and John’s responsibilities shrank dramatically.

To my surprise, though, he never treated me differently. He was disappointed–and probably at least a little embarrassed–but he never showed it.

We even became friends. He loved to go to lunch with me and Randy and swap old Donnelley stories. He loved to talk about his family and hear about ours. In a way, he treated us a little like we were his kids: rambunctious, headstrong, often foolish, never serious.

He would often shake his head and smile a rueful smile…but I always knew he liked me.

And I liked him.

In 2003 I left the company to start my own business. As often happens–at least with me–I didn’t really stay in touch. (After all, I had my own thing going on.) I emailed occasionally and called once in a while, but not nearly often enough.

Later, the parent company closed the facility and John stayed on to dispose of assets. For months he was the only employee left in the building. The few times we talked I could tell he was lonely; after all, he now lived and worked alone.

I felt bad for him…but feeling bad was all I did. And I drifted farther away.

In early 2008 Randy told me John had cancer. By the time he was diagnosed, it was too late. The disease had spread to a number of organs.

Randy said I should call.

I didn’t.

Too much time had passed. I hadn’t talked to him for years. How could I call him now? What could I say that would remotely help?

(Trust me: I know how pitiful my reasoning–my excuses–sound.)

Randy did call John. As he told me a few weeks ago, “He sounded really worn out. I pictured a thin, frail John, not the healthy, robust John we knew. I’m glad I was able to speak to him while he was still able to talk. My guilt is that I didn’t take the next step and go see him.”

Didn’t go see him? I wish that was the extent of my guilt.

I never even called.

John spent his last days in a hospice in Pennsylvania. He was laid to rest in a small cemetery in Illinois.

One day I hope to visit his grave. Maybe Randy will come along. (If I ask, I know he will come with me. Randy is that kind of guy.) I will stand quietly and pay my respects. I will tell him I’m sorry I let him down. That’s the very least my old friend deserves.

Even though any apology I make will come far too late to matter.

We all have work buddies. By their very nature work friends come and go, since those relationships are built on proximity and shared professional purpose rather than genuine friendship.

So it’s natural, when circumstances change, to leave our work buddies behind.

But sometimes work friends also become friends.

Take John. He handled an incredibly awkward professional situation with uncommon grace, not only stepping back professionally…but then stepping forward to extend a hand of genuine friendship.

How many people in a similar situation do that?

John was more than a work buddy. John was a friend. He would have done almost anything for me.

I should have treated him the same way.

Don’t do what I did. When circumstances change, and work is no longer the glue that binds a relationship, do everything you can to maintain the genuine friendships you’ve formed.

Someday you might need a friend. More important, someday your friend might need you. John needed me. I could have helped. I could have made a difference, however small.

Your friends may go somewhere else–but you don’t have to let them go.

Genuine friendships are too precious to waste. Stay in touch with your buddies…and hang on to your friends.

Jeff Haden, I Let a Friend Go: The Most Painful Mistake I Ever Made, Inc.com