I was "chubby" as a kid, and always had a weight problem into adulthood, also experiencing the yo-yo weightloss/gains from various diets. I finally succeeded in keeping the weight off, as another poster mentioned, at age 48 by eating healthier and becoming a runner.
While I don't have to obsess about food and weight like some people in the article, I do diligently weigh myself a few times per week and crack down on myself if I go north of 182 pounds. Like most people, it's easy to gain and so much more difficult to lose weight, so better to start quickly.
Besides genetics, I think the other reason diets fail is simply because once people lose the weight, slowly and steadily they resume their old habits so the weight inevitably returns. Fortunately for me, my passion for running remains high, and I remain aware of what I am eating. But it is a lifelong commitment - it is simply way too easy to have that second bowl of ice cream without forcing oneself to resist.