Or, to simplify back down from the conic section stuff, the "wall" that Beaver is describing isn't elliptical. It has the steeper the closer you get shape that you're probably used to seeing on the diagrams, and people (planets) aren't always cycling exactly perpendicular to it.

Notice how planets orbit faster the closer to the sun they get? The gravity well is steeper there, and you're lower down the well. So you get a buildup of speed from going in, which is useful because that going faster is what (might) stop you falling right into the centre. As you rise back out you slow down again, to the point where, if you're in an orbit you find youself falling back in once more.

Have I stretched the analogy enough now?