PBS has a good video on it: https://youtu.be/et7XvBenEo8?si=w2ZJDnYQbWDY3TgR

The summary is that scientists don't have a single, simple equation that they can use to precisely predict the orbits of three bodies based on the initial positions and velocities of those bodies like they can with only two bodies (the two-body problem). The solutions they have are either approximate solutions (not precise, but close enough to be useful), equations that apply only to specific types of orbits and therefore can't be used to predict other three-body orbits, and a general equation that is so ridiculously long that it is not really usable. I am also just a layman, so take my summary with a grain of salt, but hopefully the video will help.