Consider the situation that you've been putting "things that are cold" together. Snowflake. Snowman. You've also been putting "Buildings" together. House. Castle. ... And now you've got an igloo. Where do you put that? "Things that are sports like". You've got a football, a baseball bat... and now a hockey stick. Does that go in the cold things? Oh, here's a stadium - does that go in the sports area? or the buildings group? You've been putting round things together - frog eggs, wheels, and this disk with a slash through it. And now you get things that look like pills... was that thing with a slash through it a pill? Should you move it over to the pills section? or leave it with the round things? Or maybe move the pills adjacent to the round things.
So on one hand, the game is about organization of things... on the other, it's a word and idea game about how you group particular things together.