Joy of moment shattered by Boston Marathon blast

There's one image that's stuck with me from the tragedy at the Boston Marathon finish line. It's in the video of the finish, when the runners are nearing the line at the 4:09 mark. The explosion goes off, and one runner just collapses and begins rolling on the ground. Was he hit by shrapnel? Knocked down by a shock wave? I don't know, but I hope he's one of the fortunate ones.

It hurt, seeing that guy fall within literally feet of the finish line, because he was on the cusp of one of the greatest moments of his life. He was right there. This is something like what he was feeling, what it feels like to finish a marathon:

• Your body isn't your own anymore. Ever had that feeling when you touch hot water, and just for an instant, it feels cold? That's how your legs feel. Your feet? Forget it. They're bricks.

• Your arms, which have been pumping for the last two, (if you're world-class) three, (if you're very good) or four (if you're my speed) hours, feel like you've been lifting a truck by the bumper. 

• Your gut, if you're lucky, is in a state of stasis. If you're not lucky, it's convulsing, but you left shame behind 20 miles ago. 

• Your mind slips from thought to thought, bouncing from Good God this hurts to holy Christ I'm almost done to whatever snippet of song has been playing on repeat in your skull for the previous few hours. There's cotton in your ears and a film over your eyes.

• And all around you, there are cheers. Cheers like nothing you've ever heard in your life, and they're for you. Finishing a marathon is the closest you or I will ever come to standing on the field celebrating a Super Bowl win. It's a kind of ultimate but achievable physical goal, an honor and a medal you can wear for the rest of your days with pride.

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Unless you've run a marathon – and I have, though "run" may be a generous verb to use – you can't imagine the transcendent joy that washes over you when you cross the finish line. The New York Marathon finishes in Central Park, and the last time I ran it, I was crying tears of joy for at least the last mile, maybe more. (It's all kind of hazy.) Spectators, too, are moved to tears watching people find that extra gear, that extra measure of strength inside themselves.

And now, this. The sheer cruelty of this tragedy, targeting a gathering of people on the happiest day in their city, just defies imagination. And there's the possibility – certainty, really – that this will forever alter the way that these race finishes are handled. Sure, we can go with the whole "don't let the terrorists win" angle, but this is more personal. This is about how each of us can find something in ourselves that connects us to others through sports.

Road races are our grand unifying sporting events. As athletes, we won't get anywhere near the World Series or Augusta, but all it takes to join in the grand community of runners is a desire to get up off the couch.

And that's what we need to do now. Get up off the couch. Go for a run. Or a stroll. Or a walk. Whatever. Think about the people in Boston who pushed themselves to the limit, or cheered on those who did, only to have a coward strike. We can't let the bastards whose lives are failures terrify the rest of us, who want to and try to reach beyond ourselves.

The goal of a marathon, for most of us, isn't winning, but completion. Pile up the miles. Finish the run for those that now can't.

More Boston Marathon bombings coverage on Yahoo!:
Multiple fatalities, over 100 injured as two bombs explode | Twitter reaction
Photos: Explosions near Boston Marathon's finish line
Get more coverage of the Boston Marathon explosions