I've been an employer for years now. In that time, many people have come and gone. Some I've had to help out the door—I hate that. Many, though, have left because they wanted to take their career paths in a different direction, or they got lured away by an opportunity they couldn't pass up, or they've grown out of their role and there's nothing more advanced for them here quite yet.

Whatever the case, I get it. I'm happy for them, and I'm happy for the time we got to spend together, working in tandem on really exciting projects and building companies in the process.

So I'm not shocked that people leave. I'm shocked that they don't stay in touch. At all.

These aren't people who had only passing contact with me. These are people I often worked with closely, five days a week, sometimes ten or more hours a day. I went to their kids' birthday parties. I threw them wedding showers. I heard about and tried to console them through their heartbreaks. Sometimes I bent over backwards to help them out during crises.

Sure, employers and employees always have a wall between them—a need to bear in mind roles and hierarchies—that keeps theirs from being a truly unfettered friendship. But other than that barrier, I'd say we're friends. More so sometimes than other people I've only known in a very distant fashion, but who've stayed in touch for years.

Yet they leave for a new opportunity, and I never hear from them again. I might hear from their banks when they're refinancing their homes. Or hear from future employers calling for references. They might occasionally get in touch personally when they need something for tax purposes. That's about it.

A few people have stayed in touch. One invited me to her wedding, even, and that meant a lot. Another sent me a birthday note the year after he left and dropped by the office with his daughter to show me how much she'd grown up and say hello. Another sends me e-mail from time to time, saying hello, forwarding articles that she knows I'd like. Just casual contact, maintaining relations. I wouldn't expect more than that. And I do the same with them.

So maybe some of these former employees weren’t really friends after all. I get that. But wouldn’t it be wise of them to preserve relations with their former employer? Maybe for networking purposes—after all, I might have contacts that could be of value to them in the future. Maybe for reference purposes—so that, if they need a letter, I can add present-day color and current relevance to it? And definitely for general goodwill—it's always a good idea to maintain positive impressions, rather than having someone think, "Oh yeah, sure. That’s somebody that I used to know."