Very cool, if true

A fad diet that you abandon because it's too difficult to sustain, or once you have reached the weight you want, will definitely not work. Going back to the habits that made you fat in the first place will definitely make you fat again.

A permanent lifestyle change that includes long-term changes to dietary and exercise habits (not "a diet") will always work if you commit to it. How easy or hard that is depends on the individual and their circumstances, including of course their general medical condition, cultural attitude towards obesity, and the level of support they get from their society when trying to lose weight. Ultimately, it's not physically possible to put on more fat than you eat; there is no such thing as a perpetual motion machine.