Hate to disagree with you over GP, with whose comment I mostly disagree too, but:
> you fully (except in rare cases) control the factors that lead to obesity.
Not really, unless you're a homo economicus rationalus and are fully in control of yourself, independent of physical and social environment you're in. There are various hereditary factors that can help or hinder one in maintaining their weight in times of plenty, and some of the confounding problems are effectively psychological in nature, too.
> A solution to obesity is not to exercise but a varied diet, and eating less of it to match your energy needs
I've seen reported research bounce back and forth on this over the years. Most recent claim I recall is that neither actually does much directly, with exercise being more critical than diet because it helps compensate for the body oversupplying energy to e.g. the immune system.
I mean, obviously "calories in, calories out" is thermodynamically true, but then your body is a dynamic system that tries to maintain homeostasis, and will play all kinds of screwy games with you if you try to cut it off energy, or burn it off too quickly. Exercise more? You might start eating more. Eat less? You might start to move less, or think slower, or starve less essential (and less obvious) aspects of your body. Or induce some extreme psychological reactions like putting your brain in a loop of obsessive thinking about food, until you eat enough at which point the effects just switches off.
Yes, most people have a degree of control over it. But that degree is not equally distributed - some people play in "easy mode", some people play in "god mode", helped by strong homeostasis maintaining healthy body weight, some people play in "hard mode"... and then some people play in "nightmare mode" - when body tries to force you to stay below healthy weight.