Once again, you are talking about what people have to do to drop weight. Pretty sure every obese person knows what they have to do to become, ultimately, fit. What they don't know is how to get themselves to do it. You say, some just lack willpower. Well, it is the same as giving "42" as explanation. Okay, they lack willpower, now what? How do they gain one? It is much more complicated than "just do it", because people who cannot go for weight dropping do so for deep psychological reasons, which ultimately cause low willpower in this regard. A person can really want to drop weight, but they might have some other deep issues in life that prevent them from taking that route - again, listen to boogie on Youtube, he is a good example of that.
No, I did have motivation and strong will. I'd tried everything I could find. I tried exposure ("go outside and ask 100 people stupid questions"), reading motivational books, reading psychological books, trying weird mental tricks - nothing helped, there just was this irrational fear, and it wouldn't go away no matter what I did, and it was debilitating. I did every damn thing I could think of or find any information on, and nope. Because all those things didn't address the core of the issue: social anxiety wasn't just there as a random disorder, it actually covered deep insecurities I had - but no one could explain to me what they were, and I wasn't mature enough to be able to figure them out.
What helped? Simply growing up, realizing that people's opinions didn't actually affect my life much, that I can stand up to jerks and such. Can't say I no longer have any insecurities and weaknesses (hell, I have a huge lot), but that particular issue doesn't affect my life any more. All that "don't care what others think and gain confidence" mumbo-jumbo was a huge waste of time, sadly. In fact, I'd say, that advice did more harm than good, because, not being able to follow it, I thought something was wrong with me inherently, and it made it harder to get out of the old mindset.
Human characters are very complex and complicated entities. When a person has a major problem in life, it usually isn't caused by them just being bad at handling that particular problem - usually it means that there is something deep in their character that prevents them from solving this and a few other unrelated problems. That's why I hate it, absolutely hate it when someone, say, feels bad about a person online bullying them, and then someone says, "Omg, grow a thicker skin, wussy!". They don't know what skeletons this person has in their closet, what they might be going through, what old scars might be opened by the bully accidentally. Things are never so simple, and when someone has a huge problem or feels really bad, there are good reasons for that.