I was introduced to running in its first boom, just as I was a senior in high school. This was in 1970, when the world was young and I was younger yet.
One of the first things I learned was that, when you pass another runner going the other way, you acknowledge him (or her, of course). A little wave, a nod, a smile, no matter how tired you may be. You are touching the earth together, in time and, if only for a moment, in space. It's simple etiquette.
I run almost exclusively, when I'm not hashing, on the Yangjae Cheon now, and among the dogwalkers and plain old walkers and bicyclists and kids and couples there are always runners. I smile or nod or raise my hand in greeting; sometimes they respond and sometimes they don't. I'm just getting over the pettiness of being annoyed when they don't; I suppose they didn't start running forty years ago in Ithaca, New York (although why the hell not?), so probably they're not being rude, just uninformed.
But once in a while, an ajumma (stereotypical flowery-bloused, bevisored, chattering middle-aged lady) who's never run a day in her life will smile at me, or a man old enough to have fought in the war here will shout "USA Number One!" And that makes up for a lot. We're all on the same team, you see.
And when I finish the Joongang in November, the first thing I'm going to do is stagger back to the last hundred yards of the course and cheer for the people behind me. It's what you do.