Inertia (the tendency still objects have to stay still and moving objects to keep moving) helps too. A tightrope walker weighs quite a lot. That means they have a certain amount of inertia and it takes quite a bit of time for their body to move to one side or the other. If they feel themselves tipping, they have enough time to move another part of their body (or a stick or umbrella they're carrying) to the other side. That produces a tipping force in the opposite direction that keeps them balanced. Looking at a tightrope walker who's momentarily stationary, you might think no forces are acting—but you'd be wrong. Gravity acting on a walker's left arm will try to make him tip to the left, while the weight of his right arm will tip him to the right. The walker stays perfectly upright, perfectly motionless when all the different turning forces are exactly balanced and canceling one another out.
If anyone asks me what "Gravity" is about, I'll tell them it's a tense adventure about a space mission gone wrong, but once they've seen and absorbed the movie, they'll know the truth. The root word of "Gravity" is "grave." That's an adjective meaning weighty or glum or substantial, but it's also a noun: the place where we'll all end up eventually. The film is about that moment when you suffered misfortune that seemed unendurable and believed all hope was lost and that you might as well curl up and die, and then you didn't. Why did you decide to keep going? It's is a mystery as great as any in physics or astronomy, and one we've all grappled with, and transcended.