Thank you so much for your kind words!
It took me over 5 years to write the book.
I would compare it to running a marathon-sized distance. A marathon is about 26 miles. In one day, it would be very fatiguing. But over 5 years, it would only be 5 miles a year. That is less than a half a mile per month. It would be less than an 1/8th of a mile per day on average. That's nearly nothing.
With that said, I can exhaust and fatigue myself mentally without writing a word. I can do it just sitting quietly on my porch drinking seltzer water. And I do sometimes.
I think I like it. I workout in the gym everyday too. I enjoy working out in the gym, or mentally on the computer or some other project, until I'm fatigued. I enjoy challenges. I enjoy exercising both body and mind such as by testing myself by lifting ever-higher amounts of weights in the gym until failure or pushing myself to endure ever more levels of discomfort or endure ever-higher levels of pain. I do it for one thing as an exercise to increase my physical limits (both mental and non-mental) gradually over time. But I also do it because I enjoy facing the challenges in the present and pushing myself to my limit in the present. Even if I knew I was going to die tomorrow, I'd probably still lift weights today; it might even motivate me to work out harder and longer to hit new PRs in the gym since it would be last chance.
I love boxing, for example, and regularly spar with my friend. Win or lose, I love going out there with the gloves and doing my best at something so challenging and fatiguing. There is something I find so beautiful about pushing one's body and mind towards their absolute limits Part of it, I think, is that those limits always seem to be surprising more than we think. When we go as far as we can, I think we tend to be surprised how incredibly far we can go. When we genuinely do our true best, I think we tend to find our best is shockingly much better than we had thought.
If anything, when it comes to these kinds of things, I do them and I like doing them not despite them being fatiguing or painful, but rather because they are.
Thank you for your thought-provoking question!