system
Given the following post, respond as if you're commenting on Reddit:
human
How does orbital resonance really work? What causes them and why are some unstable?
gpt
Lets take, for example, the Kirkwood gaps in the asteroid belt:

For asteroids in the asteroid belt, the biggest influence on them by far is the force of gravity from the sun. There is, however, a very minor effect from the gravity of Jupiter. Because force is proportional to the inverse square of distance, we can model the effect of Jupiters gravity as a tiny nudge that occurs when the asteroid and Jupiter are at their closest.

If there is no orbital resonance, this kick always occurs at different points in the asteroids orbit, so the tiny kicks do almost nothing. If the asteroid is in orbital resonance with Jupiter, then those kicks occur at the same spot in its orbit each time, and can, over the course of a few million years, amount to a huge disturbance, resolving itself when the asteroids orbit is either sufficiently perturbed so that it leaves the resonance, or it hits something, or it is flung out of the solar system.

However, not all orbital resonances are unstable. Sometimes, the regular boost is such that it will act to oppose deviation from the resonance. Some examples are Jupiters moons Io, Europa, and Ganymede are in a 1:2:4 orbital resonance, and Neptune and Pluto are in a 2:3 orbital resonance. Arguably, the stability of the Lagrange points could be called 1:1 orbital resonances, but that is kind of the is-a-hotdog-a-sandwitch of orbital motion.