The play on Joel's maxim is a little forced, but here's the real "ouch" for me:
But working with them directly will show you when they're better. It's the only way. You'll gradually realize that your math deficiencies aren't just something that you might need to beef up on if you ever "need to"; you'll see that virtually every problem space has a mathematical modeling component that you were blissfully unaware of until Done, and Gets Things Smart gal points it out to you and says, "There's an infinitely smarter approach, which by the way I implemented over the weekend." You stare slack-jawed for a little while, and then she says: "Here's a ball. Why don't you go bounce it?"