Abstract. People like identifying and naming the things they see. It's an oak, not just a tree, a hawk, not just a bird, and a tiger, not just an animal. I'll tell you how to identify and name the 17 symmetry patterns you can find on floor tiles and wallpapers all around you (yes, there are exactly 17 of them, no more and no less).
A video version of a similar talk is at Treehouse.