Devora Zack wants you to stop multitasking right now. In fact you weren't even multitasking; you were task switching. Moving from one project to another always requires a mental reset, and, even if it's only momentary, those moments add up and take time out of your day. Instead, put all your energy into one task at a time. You'll get more work done better by doing what Devora calls singletasking.