The human brain does not thrive in a grey zone. It prefers to work in binary terms. On/off. Awake/asleep. Eating/fasting. Working/resting.
The modern world conspires to push us away from these extremes and ever closer to the middle. Instead of spending some time at 100 then some time at 0, we are encouraged to stay as close to 50 as we can all day long. If we do not resist this unnatural progression, we risk becoming mere shadows of our ancestors.
When you’re doing something, really do it. Go all out as though it’s the last thing you’re ever going to do. Then when you switch, really switch.
This is how nature intended it, and the last hundred years of scientific progress isn’t going to change that.