Comment by lambdasquirrel

The research on this is not new, and it’s not as simple as this. If you give people a task that’s well-rehearsed for them, that they’re good at, they’ll tend to do better. But if you give them something less well-rehearsed, something that’s “hard,” they do worse. I wish I had my psychology textbooks on hand for the references, but a lot of this stuff isn’t obvious until after-the-fact.