The best athletes train hard in short bursts then rest and reflect on their training.
How could they improve it?
Do they need to increase the intensity? Is their nutrition where it should be? Is the recovery adequate?
The best knowledge workers do the same.
They have intense periods of study and learning and then rest and reflect.
Rest may be doing nothing. Reflecting may be teaching or building something with their knowledge.
Like muscles and reflexes, knowledge grows during rest. And like how the best training programs adapt over time, the best minds are always thinking of new ways to learn.