Motivation is Irrelevant

Motivation is irrelevant if you enjoy the activity. The goal is to make bodybuilding, weight loss, cooking healthy, or really, any projects or skills enjoyable to do/learn so doesn't feel like a chore. As long as the reward/pleasure is greater than the pain (time/money/energy invested), people will keep doing something towards a goal consistently or for the time doing it.

It's call the act of "play". Like you never need "willpower" or "motivation" to learn how to play the guitar or tennis when you were young, nor do you call it "exercising". You simply love it, so you do it, even on a cold day with sore ankles.

If you keep struggling with falling off diets and training routines, it's probably because you're investing too much of your resources (pain) on the wrong stuff (I call them fluff), therefore, making pain greater than the reward. This is when you need to re-evaluate your approach.

Why do you think you have to run 2hr/day everyday when someone else can do it without? Why do you think your skinny friend can eat pizza and margaritas every weekend and not get fat while you feel every cupcake you ingest seems to go straight to your butt? Why do you think you have to spend 60$ gym memberships and 100$ on supplements every month when others can do it while actually save money on grocery? How do others do it so effectively and painlessly and you can't? and please, your excuses aren't good enough because others have done it in much worse conditions. 

It's sad most people who go to the gym, looking for diets online, and youtube/momblogging/meathead bro trainers will never learn this. Invest your resources on real-world, result-driven, practical instructions so achieving your fitness goals would feel like a spontaneous effort.  When what you need to do to reach your goal is fun/rewarding (or with less pain) every step of the way, than you'll actually enjoy the process.  When you enjoy the process, motivation is not required.