There was an article on HN a while ago saying that basically the secret to productivity is ... slack. In other words, excess capacity.

I used to have a tight schedule switching from tasks to learning to meetings to more tasks and more learning, 50 minutes work, 10 minutes break, relentlessly, like a robot.

Then I realized I'm not a fucking robot. Now I work 2 hours per day at most. Complete my tasks and can do this shit in a sustainable way as opposed to burning myself for what?

I'm super engaged. For two hours tops :D