Cal Newport, New York Times Bestselling Author of Seven Books

I build my days around a core of carefully chosen deep work, with the shallow activities I absolutely cannot avoid batched into smaller bursts at the peripheries of my schedule. Three to four hours a day, five days a week, of uninterrupted and carefully directed concentration, it turns out, can produce a lot of valuable output.

Deep work: "Professional activities performed in a state of distraction-free concentration that push your cognitive capabilities to their limit.