What allows some people to stick to their diet while others fail? It would seem logical to say some people have more willpower/discipline than others right? Well if they have more of this why are they out of shape in the first place.
Going a level deeper maybe it is because some people are just more responsible about their body and health than others…but that begs the same question as above, if so then how did they get off track?
Maybe it’s just easier for some people right? Wrong. Half the answer is different for everybody and half is the same for all.
Continued in part 2: https://wefit.ca/2021/02/23/diet-glue-part-2/
wefit.ca 
“Why did they get out of shape in the first place?” I’d hazard a guess that it’s perhaps because their priority wasn’t on “being in shape” at an earlier stage. Now that it is, those successful folks are more inclined to use their willpower/discipline/responsibility (whatever) to help them get back on track and back to that state that they neglected for so long.
As said in the other response the key doesn’t seem to be force of will or any such self imposed energy.