I Wish My Wedding Ring Was a Bag of Golf Balls

If you're a big blob of material and you're too close to a planet, you cannot form a moon because the planet will just keep tearing you apart. But if you're far enough away, then you can form a moon. So past the Roche Limit, you get moons closer in than the Roche Limit,. You get rings - Saturn's rings are too close to Saturn itself to form the moon. And so that's why the moon is a moon.