> people who aren't willing to massively restrict their diet and live in discomfort for the rest of their lives
I also take issue with this statement. Many fitness motivation images on the Internet talk about rejecting temptation to work towards your goals. As I was thinking about this comment, I was reminded of Ben Stiller's pizza scene in the movie Dodgeball [1]. Jokes aside, the scene is a hyperbole to how even fit people are susceptible to temptation and take actions to not giving in. Not to Stiller's degree, but I can distinctly remember times where I just stare at the ice cream aisle with grocery shopping. It is my own mental discipline to not buy it. Quitting World of Warcraft to get in better shape is also a part of my past. Shifting to an active lifestyle is hard, it has a difficult initial start, but persevering through it has helped me become the healthier person I am. I also recall Jesse Shand's transformation [2], where I believe one of the phases of his weight loss was simply reducing the number of fast food meals he'd consume in a single sitting (instead of 8, only eat 7, etc).
I will assume that formerly obese people have higher cravings. No doubt a former heroin addict has cravings. I will accept that it is harder for these individuals. But again, that does not mean you shrug your shoulders and say "that's the way it is".
I’ve known people to be naturally skinny or even tone but not “fit”.
I never really understood why this was always a catch-all trump card. So you can't gain/lose weight as easily as others. In my mind that just means you need to work harder rather than shrug your shoulders and say "nothing to be done". Specifically its people doing this that never look into their diet or are willing to change any of their habits.
Slightly related but Carol Dweck's growth mindset for education is literally this, but the difference is in people who believe they can't get in better shape and people that can.