I am not a physicist. I am a writer, runner, and recovering bass trombonist. But that doesn't stop me from thinking that I understand physics. I've read about a concept called "The Butterfly Effect." The definition goes something like this: Small variations of the initial condition of a dynamic system may produce large variations in the long-term behavior of the system. It suggests that a butterfly flapping its wings in Hong Kong can eventually affect the weather in Kansas. Cool, huh?

It got me thinking about how small variations or changes in our lives can have unexpected long-term effects. I used to be an overweight smoker who didn't exercise, but small decisions over the years—like going for that very first run—have produced large variations in my long-term behavior, helping me become the 45-time marathoner I am today.

That transformation didn't happen overnight. It didn't happen after one run, though many of us expect just that. We think that every run needs to produce some immediate benefit. Whether it's supposed to make us faster or build our endurance, the effects of today's run are supposed to take effect, well, today.

I think that's why many of us like to sprint the last quarter mile of our daily run. We like the feeling that comes from a hard effort. It feels like we're accomplishing something. (By the way, that final sprint at the end of a run is a good way to pull a hamstring. Trust me on this.)

What I didn't know then was that there is a Butterfly Effect in running. It isn't the grand gestures and epic achievements that make us runners. Sure, running for 30 minutes nonstop is great. Qualifying for Boston is great. But that's not ultimately what makes you a runner.

It's the little things we do every day adding up over time that matter. It's not just running one morning; it's getting up morning after morning and running. It's not just eating better at one meal; it's making better decisions at every meal. It's the small decisions we make almost without thinking that make us runners.

The lesson from today's run may not be important right away. Learning you're more comfortable wearing a long-sleeve shirt even when it's not that cold out may lead to the best race of your life years later. Learning that you shouldn't have eaten the Firebrand Salsa on your nachos the night before a long run may mean a marathon PR somewhere down the road.

It may be a function of aging, or it may be a function of maturing as a runner, but knowing I don't have to squeeze significance out of today's run has made running much more satisfying. Today's run might just be a r