what's wrong with this picture?

So, you know how it is when you're writing a scene and everything's just humming along with dialogue, setting and characters just kind of clicking in place? Right. Well that's not what's happening with the scene I'm working on now. It's been a bitch to write, but the good news is, I figured out why. The scene has two fundamental problems that I somehow didn't notice right away.
First of all, I had a huge coincidence where my secondary character just happens to show up at around the same time my two main characters arrive on the scene. The guy has a reason to be there--he's visiting the grave of a family member--but what are the odds that he'd turn up just when my two heroes do?
Second, I didn't give my secondary character a clear goal. Sure he's got a reason to be where he is, but that didn't give him a strong motivation to interact with the main characters. So, when I got the three of them talking to each other, the dialogue kept coming out all rambling and stilted. No wonder!
The thing that bugs me the most about this is that I spent literally hours plugging away on this scene, patiently rewriting in hopes that it would suddenly start working. So, I hereby promise myself that from now on, whenever I find myself slogging away on a scene that doesn't work, I will step back and go through the following checklist of super-basic questions:

1). Logic: Does the situation make sense? Do the characters have a reason to be in that particular place, at that particular time, doing the things they're doing?

2). Coincidence: Does anything in the scene happen by chance? Not that coincidences are always bad, but they should be there for a good reason. (Hint: laziness on the author's part is not a good reason.)

3). Goals: Does each character (or group of characters) have something that they're trying to accomplish? This doesn't have to be saving the world; maybe your character just needs bus change.

4). Conflict: Are the goals of one character (or group) in opposition to what the other side wants? And this doesn't have to involve explosions; maybe the character who wants the bus change could get into an argument with a coffee shop owner who doesn't want to give it to him.

5). Stakes: Do the characters care about the outcome? If the bus-change-seeking character misses his bus, will he be late for something important, like a date or an appointment with his parole officer?

Pretty obvious stuff, you say? Well, yeah. But it's the obvious stuff that tends to slip my attention when I get caught up in the minute details of writing a scene. And when I run into difficulty, my tendency is to just work harder at the thing that's not working. Sometimes that's okay; sometimes I do just need to plug away at it. But even then, taking five minutes to run through the checklist couldn't hurt. In fact, I think I'm going to change my resolution: from now on I will run through the checklist *before* I start writing a scene, and maybe I won't run into so many snags in the first place!