I am trudging through a drizzling rain when I come across this wooden footbridge I’ve never seen before.

Well, that’s not exactly true. I’ve driven this stretch of road a thousand times to the doctor’s office, the mall. So surely I’ve seen this bridge a thousand times, too. But obviously, I saw it in the way you sometimes see things when you’re driving past at 45 miles an hour, which is to say, not really. Your focus is the destination, not the journey.

But walking is different, slower. And this early morning, deep into an 18-mile hike, I find myself noticing things I’ve never really noticed before. A lake not quite visible from the road. A sidewalk curving gracefully beneath an overhang of trees. And this wooden footbridge over a small, shrub-filled hollow.

It is your fault I am out here on a miserable Saturday morning when even the sun is sleeping in. Back in April, I used this space to announce my participation in the Washington, D.C., leg of the annual Susan G. Komen 3-Day For The Cure, a 60-mile, three-day walk to raise money against breast cancer. I don’t do bake sales, so I’d hoped a few of you would sponsor me, and I figured I’d contribute whatever more was necessary to reach the mandatory $2,300 minimum.

Six months and almost 500 donations later, my tally stands north of $27,000. You guys are amazing.

And motivating. When I first started this, I was spurred by a fear that, come the big day, I would end up bent double after the first couple of miles, gasping and wheezing while some 82-year-old lady with a walker stumped by, yelling, “Quit hoggin’ the road, sonny!”

Now my greatest fear is of returning to this space to tell people who donated 27 large in my name that I couldn’t close the deal. Which is why, every spare moment, I’m training like Rocky.

The walk will be Oct. 8-10. As it happens, the day after is my 53rd birthday. That doesn’t qualify me for the senior discount at IHOP, but it does mean I am of an age to contemplate some of the grand sweep of this life.

Lately, I have this theory that we live in three great arcs. The first 25 years are for coming of age, figuring out who you are, getting an education, starting a career.

The next 25 are for rat-racing, raising your kids, paying a mortgage, building a life.

But from 50 until … that’s for having some fun, for trying something new, for being of service and for doing some of those things you always said you’d do, someday.

As I said, it’s a theory. But sometimes life is like driving a car. You are so focused on the destination that you keep getting to places without realizing how you got there. When did my youngest child become a woman? How is it that high school will soon be 40 years past? And what happened to those things I said I’d do someday?

I always said someday I’d walk to raise money against breast cancer in honor of my mom, who died of the disease in 1988. That’s an easy thing to say. Not so easy to do. Each year, I found perfectly logical, rational reasons to talk myself out of it, not least of which is the fact that I am more sedentary than your average boulder. I’d have to be crazy to think of walking 60 miles.

And the truth is, I probably never would have done it, except that one day, I just did: I snuck up on myself, signed up without giving myself a chance to talk me out of it.

Now myself is wondering if I’ve lost my mind. Myself keeps reminding me that we don’t do things like this.

But you know, you get tired of getting places and wondering how you did. Life is an act of will. Life is conscious decisions, including the decision that maybe “someday” has waited long enough.

And life is an understanding: We’re all going to the same destination. The only difference is in what you choose to see along the way.