These are two things I think about every once-in-awhile. Usually late at night. While drinking. Heavily.

Also I think about them while writing code. And typically, when I have to make a decision between one or the other, I choose the wrong one. Probably because I’ve never deeply thought about them in an IS-A versus CAN-DO relationship as outlined here.  Which, despite the broken English, is the best overview I’ve ever read on the difference between the two.