Every five years or so, I run into my high school classmate Ellen. We live about three miles apart, in neighboring communities -- not unusual, except for the fact that we are 150 miles away from our hometown. We just happened to have landed in the same area.

The first time, we bumped into each other was in a supermarket parking lot. Another time it was at a Dunkin' Donuts. Last Friday it was on a train from Boston. I was standing up to get off at the next stop when I spied a woman in sunglasses, three rows ahead looking at me as though I was a ghost from her past, which, of course, I am.

Ellen and I have always taken these serendipitous moments as a gift. When we had the time, we sat down over a cup of tea or coffee, to catch up on our lives. And that's what we did on Friday. As always, I came away renewed and energized.

Why is that? I wonder.

I think there are three reasons.

First, we share common roots. Our class had only 71 students, so everyone knew everyone. We can talk about classmates like Mary Beth, Dave, Bill or Bruce, or teachers like Mr. Mercier, Mrs. Holmes and Mr. Duquette. We attended the same crepe paper prom (not together). Such are life-bonding experiences.

Second, other than my family, there are few people who knew me nearly 40 years ago, when my personality and character were still being formed. Ellen and I knew each other when we were 16, 17, 18 -- younger than our children are now. And there's an unspoken allegiance, I think, between classmates, to keep secret some of the things we remember.

Third, we have traveled similar paths since high school. Our children are the same ages. Our marriages are about the same age. We have entered the same empty nest phase and are trying to figure out what's next.

So, when I check in with Ellen, I'm checking in on myself, too. And, from what I heard on Friday, I think we're both doing pretty well. And that leaves me feeling renewed and energized.