Thanks, this is a really interesting discussion
I am familiar with David Goggins. He is quite amazing. I think what he does in some ways is mind of human body, but in other ways is an expression of human nature.
Let me explain. I was probably not very clear in the post about this part on human nature. Homo Sapiens evolved to adapt to a certain environment. The 290,000 years before the Agricultural Revolution were spend in an environment quite different than the world today. We as a species are exquisitely adapted to survive and thrive in that environment. This is why we have conquered the Earth.
When I say human nature, I mean our biases, blindspots, logical fallacies that are adaptations to that environment. In essence a model of the world that still believes (unconsciously) we are in that past Paleolithic context. When I say fight human nature, I mean fight impulses that come from those adaptations. Impulses which are not beneficial now, such as being sedentary, but were in the past (when it was advantageous to conserve energy as much as possible).
My conclusion was that in the past I thought I could fight this past model (human nature). But now I realize it's not a game anybody can win, except for very short periods of time.
Rather I believe the solution is to change your environment and your model of the world, so that those unconscious biases (human nature) pushes you to behaviours which are beneficial.
To come back to the sedentarism example: instead of attempting to move from doing nothing to intense exercise 6 times per week (which is what everyone does), to make it a gradual habit: like at least 10 minutes of running at the same time every morning before your cup of coffee. This habit will naturally grow into a bigger habit. You are using your human nature to reach the outcome. In this case instant gratification (coffee after), habit formation (same trigger every day), overcoming resistance with minimum dose (only 10 minutes).