Or mental effort… It is often much harder than physical effort. I say this as someone who has experienced both types of effort at an intense level.
I learned almost the entire high school curriculum for the baccalaureate exam in just six months before the exam because I hadn’t pushed myself during the four years of high school. My head ached from so much studying. I had set myself a study schedule with breaks. My brain felt like it was cracking from how much I was learning. But I studied, and I passed the baccalaureate.
The same thing happened during my military service. Even though I was completely exhausted during training—I served with the firefighters, the toughest branch at the time, where training was extremely harsh—even though I was utterly drained, I still managed to push forward and continue the training.
Now, in the present, when I engage in both types of effort, I realize that physical effort is easier for me to start. I can mobilize myself more quickly. But when it comes to intellectual effort, it’s harder. It drains me faster and it’s more difficult to get myself going.