If there’s one thing we should all take to heart, it’s that humans are strange: They rarely behave the way we expect (or want) them to. Testing often reveals issues we would never have found out by merely thinking about a design. Conversely, something that looks wrong might actually work perfectly well.
via ignore the code – Opinions vs. Data. The fallacy with intuitive guesses is that they are intuitive and not based on real data most of the time. Testing can sometimes reveal things that you wouldn’t have normally guessed.