There’s also an implicit requirement that a planet must not be so big that it starts nuclear fusion, because then it would be a star. That’s part of its being. And furthermore, the IAU says a planet must orbit a star instead of going rogue or orbiting another planet. That’s more of its doing. This mixed-up set of being and doing requirements reflects the chaos of human history, because we didn’t understand what planets were in the earliest days of astronomy, and we never said, “let’s just start over and create a completely new system that makes sense.”