Tim, that quote makes sense only with a broken debugging cycle.

If you write your code bottom-up and debug it as you go, then it simply doesn't make sense to talk about writing clever code you can't debug. If you can't debug it, then it wasn't clever in the first place -- it was just something that didn't make sense.

Taking it literally, this is like saying "Writing a novel is easy. Rewriting it so it isn't completely boring worthless drivel is harder."

Still, there's a worthwhile thought in it. If you try to do something clever that you don't completely understand, it's likely to be easy to make mistakes.