To be elegant, you want things to be composeable, and you ideally want them to compose in a natural, simple way. When designing feature "A," you shouldn't have to write special case code for composing A with B and A with C. What happens when you add "D?" Are you supposed to go back and retroactively change A, B, and C to compose with D?

Special case code is often a sign of *inelegance*, a smell that the model is not right. I've written a lot of inelegant code. For example, I was recently working with adding some functional idioms to JavaScript.

(Although these examples are in JavaScript, I don't think the concept of inelegance is JavaScript-specific.)