[jkbyc]

The Lesson to Unlearn http://www.paulgraham.com/lesson.html (I think)

[cjenkins]

I'm pretty sure that's the one! Takes a bit to get to the punchline but the idea that you want to look for tests that are unhackable is the big idea (and making a good product to get lots of users is the exemplar for an unhackable test).

Thanks for finding that!