Sometimes. Kids don't have a choice for example.
My brother used to coach pee-wee football and morbid obesity was a big problem with kids coming from spanish families. The issues was that, in those households, food was seen as a pacifier/reward/preparedness mechanic. One kid who was about 70 pounds over weight was, on game day, essentially getting three course breakfasts, would go to the game and play (he was O-line), have a snack immediately after the game was over, have another 3 course meal in the afternoon because "of course you need it, you missed lunch", have ANOTHER 3 course meal for dinner, and if he got remotely peckish before bed, his mother would cook him something. Now this is an extreme case, but it's one that shows that people often don't get to choose what sort of things go in their body. No one in that family thought they were doing anything wrong, it was simply how they were all brought up. If you are a kid especially, the adults in your life have to really put a lot of effort into making sure you're eating healthy, and if they don't, the kid is going to see no reason to, because you're a kid and you'll eat pretty much anything.
And dieting, in my experience, is the hardest thing about staying fit. I love food too much to go on a super strict diet, but I still try to do little things here and there, like cut out soda, drink more water throughout the day, cook my own meals with natural incredients, stay away from HFCS, stay away from fast food, little things here and there that otherwise would pile up.