Each time your brain moves any part of your…
Page 69. Each time your brain moves any part of your body, inside or out, it’s been some of its energy resources.
— from Fuel (Energy)
In the book
Here is the part no one teaches you — your brain's single most important job, running quietly under everything else, is to predict and manage your body's energy so that you stay aloft. Every movement you make, inside or out, spends some of that reserve. You are always, whether you notice it or not, managing a finite supply. — Fuel (Energy)