Hi Gregg,
Hard questions to answer. What makes me lift the camera varies. All I can tell you is that when I have a camera in my hand I go around framing what's out there. If what's within a frame strikes me I lift the camera and shoot. I miss a lot and throw away a lot of flubs, but that's all part of the game.
The main thing about this picture is that there was a fairly intense discussion going on between these two guys, and as the vendor made his gesture I raised the camera and shot. The framing was going to work too. Which made it more than a random people shot. It's a long way from a great street shot, but it IS a street shot.
I can't remember ever positioning myself for a composition. I compose on the camera when I get it to my eye.
What I do most often is simply go out on the street with a small camera in my hand -- shoulder strap wrapped around my lower arm -- and walk. The bottom line is what Cartier-Bresson said: "Photographing is nothing. Looking is everything." The other important thing he didn't mention is that you learn composition by studying thousands of great paintings and photographs. You're not going to try to copy what's been done before, but what you learn from those studies is what moves you visually, and how to place things in a composition.
The best explanation of all this probably is in my "On Street Photography." It's on my web, but LuLa also published it with some pictures at
https://luminous-landscape.com/on-street-photography/.