Doing the “hard-start” technique allows you to use your brain as a sort of double processor. Your diffuse mode can take over on the hard problem as soon as you drop your focus on it. While the focused mode is tackling the easier problem, the diffuse mode works in the background on the other, harder problem. If you wait until the end of your test session to focus on the hardest problems, your focus prevents the diffuse mode from going to work.
