These resources are expended during deep work, concentration and willpower/discipline expenditures (including starting working and maintaining work cadence).
These resources deplete and once they are low, it is difficult or impossible to start or maintain work on high-value tasks.
They can be recharged
This approach uses a simple, regular habit of deep work which removes the need to decide when and how to go deep (this easy transition conserves willpower and concentration).
The Rhythmic practitioner does some deep work every day at the same time for the same duration.
This style is not for the novice. It requires either vast willpower reserves or expert transitioning skills in order to snap into deep-mode at a moment’s notice.
Being freed from the requirement of directed attention and experiencing interesting, undemanding stimuli is restorative to Willpower and Concentration are finite resources.
By the evening, you’ve exhausted your deep work capacity (Willpower and Concentration are finite resources) and will likely work on low-value, shallow tasks. To make matters worse, by doing so you are necessarily deferring the energy recharge you could be getting - thus endangering your potential to do meaningful deep work tomorrow.
Willpower and Concentration are finite resources. Downtime, and especially spending time in nature, helps improve the ability to concentrate in the future.
There are productivity-related Impacts of directed vs free attention.