I'm gonna have to disagree with this. There are people who eat tons all the time and stay skinny without much effort, and there are people who put in tons of effort, really watch their diet and workout, but simply can't achieve skinniness. And there are all sorts of people in between. The problem is doctors, nutritionists, food industry lobbies, and government nutrition guidelines tend towards a one-size-fits-all approach to weight management, and advising people in ways that benefit themselves, not the individuals. You really have to do your own research, and try a lot of different approaches to figure out what works for you. It's really not just as simple as calories in calories out.