Unstable arrangements naturally collapse into stable ones. Eventually everything gets stable.
We are lucky that our stable arrangement happens to have a planet with surviving water within the habitable zone and with a few elements in the system that make collisions less likely. (Both the Jupiter and the Moon "sweep" space so that collisions with earth are much less common than they would be without them.)
Of course, the anthropic principle is in full force. The earth had to be lucky for you to stand on it wondering about how lucky it was -- so, if it hadn't been lucky, you would not do so and maybe some green-skinned alien halfway accross the galaxy would spend time wondering how lucky his planet was.
We are lucky that our stable arrangement happens to have a planet with surviving water within the habitable zone and with a few elements in the system that make collisions less likely. (Both the Jupiter and the Moon "sweep" space so that collisions with earth are much less common than they would be without them.)
Of course, the anthropic principle is in full force. The earth had to be lucky for you to stand on it wondering about how lucky it was -- so, if it hadn't been lucky, you would not do so and maybe some green-skinned alien halfway accross the galaxy would spend time wondering how lucky his planet was.