When my twin grandchildren were born, my son and daughter-in-law worried that they would never get past the constant care and feeding of the babies, the lack of sleep, and just the general chaos. I told them that, from my experience as a parent, the days were long but the years were short.

I was reflecting on this when I realized that the end of 2006 marked the end of my 15th year as a runner. Fifteen years! I can remember when I first started running, I would hear people talk about running for 10 or 15 years and think, How is that possible? At that point, I was struggling to run consistently for a week at a time. I couldn’t imagine how anyone could keep it up for a decade and a half.

As it turns out, running is a lot like parenting: The days are long, but the years are short. In my early years as a runner, I could recall in detail nearly every one of my runs. And if I didn’t remember all the specifics, I could always look them up in my logbook where I painstakingly recorded every mile completed.

In the beginning, I could also describe at length my preparation for and participation in every race I attempted. From my first 5-K–the Balloon Race in 1992, where I went out too fast and crashed and burned at the finish–to the Half Ironman triathlon in the spring of 1995 where it was so hot on the run that I started hallucinating, I knew exactly how I had trained, what I ate, drank, and wore on race day, whether or not I got any sleep the night before, and how I had done in the event.

Now, after 15 years, I’d guess I’ve run about 15,000 miles–although don’t hold me to it. And I’ve lost count of the number of races I’ve done. I can’t even remember how many marathons I’ve run, let alone how I trained for each.

To be sure, there have been perfect days and great miles, as well as horrible days and awful miles. There have been times when I couldn’t wait to run and times when I couldn’t believe I had to run (as well as times when I simply refused to run). And there have been runs I wished would never end and runs that seemed they would never end. During the latter, I’d often toy with the idea of collapsing just so that I could get a ride back home.

But even the longest runs end. Even the worst races are over eventually. The days and the miles and the races keep adding up. And before you know it, you are someone you never expected to be. You are a runner.

And as a runner, you keep heading out–again and again and again. Because with your first step you may have become a runner, but it’s with every step you take after that you stay a runner. And if you’re lucky, like I am, one day you’ll wake up and 15 years will have gone by right underneath your feet.

Waddle on, friends.