Sometimes you get that feeling that "life is passing you by." Which I suppose is true. And you are passing through life too. Sometimes life is like a river! Sometimes you feel right in the flow of the river, and river is carrying you along, and everything is cool. Then there are times that river rushes right over you, and you are flailing around gasping for air.
And then sometimes you crawl over to the shore and just sit back and watch that river flow. That's kind of the writer's perspective. You're not in it, but you see it, and imagine you are, or you imagine someone else is in there, or maybe you imagine another river all together. Or maybe you imagine a mountain range instead.
But whether you are in the river or not, the flow continues. So, yes, on the shore, you imagine being in the "center of the river," but the river has no center. And it is passing you by...