The common mistake -- or maybe it can be called a misunderstanding -- is that the driver tries to judge their vehicle's width by what they can see over the right side, not by where they are in the street.

On many residential streets without a painted center line, I know that if I've got my left wheels just off of center, I still have a few feet of space to the cars parked on the right.

I've been surprised myself sometimes (and in less risky situations, such as squeezing between small cones bordering a parking lot) by how narrow my car really is. SUVs (Hummers excluded) really aren't a whole lot wider, either; they're just a lot taller.