There is something about the lines painted on the road, isn't there? I catch myself doing it about as often as I catch myself being annoyed with someone else for doing it: treating those lines painted on the road like they're magic, inviolable force fields, like the line you drew down the middle of the back seat on long car trips - this is MY side and that's YOUR side, and . . . Moooooooommm!
Take the white line that marks the bike lane off from the rest of the road. I'll be rolling along, and notice a car, maybe thirty feet in front of me, with a wheel just edging over the line as it takes a curve. "Get the heck out of the bike lane," I think grumpily, before remembering that it doesn't matter to me anyway, the car's miles off and not in anyone's way. But my magic white line's been crossed; the bike lane is my safe space, it's not for cars. It's the same when there's debris in the lane or a set of potholes - it actually takes a little extra act of will to cross the line into the car lane.
It must work the other way too, since very often I'll be on a four-lane road and a car will pass me a little closer than I would like, having scootched over enough to give me clearance but apparently unable to cross into the leftmost lane, even when it's wide open. (Being a cyclist means that when I'm driving I actually do move over into that lane to give other cyclists as wide a berth as possible, because I remember the number of times I've grumbled to myself, "you had a whole other lane you could have been in, did you have to pass me so close?"
It's one of the reasons, I think, that I've found it so much more comfortable to take up more of the lane. Once a driver has moved far enough over that the tires cross that magic line, the spell is broken. In for a penny, in for a pound. Often once the line's been breached, it seems to me, drivers don't have as much of a problem moving all the way over. And so when the side of the road is really broken up, or potholed, or the drain covers are really sunken and hard to ride over, I move far enough out that they just can't get past me without crossing the line. And miraculously, cars start changing lanes to pass me instead of trying to squeeze between me and "the magic line that must never ever ever be crossed."