It’s human nature to want to classify things, to argue that baseball is a sport, but bowling is not. Before you can sort, though, you need to clarify what your categories are. Figuring those out is often the hardest part.
Mathematicians understand this as well as anyone. It’s barely an exaggeration to say that their main enterprise is sorting. The impulse goes back to at least the ancient Greeks, who established that while there may seem to be a never-ending variety of solid objects with identical faces (so-called “regular” polyhedra), only five exist: the tetrahedron, cube, octahedron, dodecahedron and icosahedron.