npsimons's Journal: Re-usable vs Re-editable

Given the recent controversy over Prof. Knuth's comments, I'm left pondering one (of many) questions: why can't code be both re-usable and re-editable? (no, I haven't read the article)

Are re-usable and re-editable code fundamentally opposed? Would it just take too much time (or genius) to make code both re-usable and re-editable? Or is Knuth just calling designing for re-usability a waste of time like unit tests?

To me, the re-usableness and re-editableness of code seem orthogonal. You can write code that is re-usable but completely un-editable (it's usually unreadable at that point). If you're writing code properly, it seems to me that re-editable is a given. Re-usable is more difficult to do, but it seems like a good idea, and a best practice that most programmers should try to get into the habit of (just like writing re-editable code).

Maybe I'm just missing something here, but I always aim to make my code re-editable and re-usable, and one doesn't seem to get in the way of the other, other than competing for my time. Thoughts?