I think some people have a propensity to gain weight 'more easily'.
In the way that alcoholics have an abusive relationship with booze, I (and I believe many other people with a 'weight problem') - have an abusive relationship with food. Like drinking to excess, this is a 'learned' behaviour : which is why many alcoholics are, I understand, the product of a home in which a parent was an alcoholic. We learn what and how to eat in childhood, and I wondered if anyone can trace their 'problem' back to a parent, grandparent, auntie etc? For example : My OH is also very overweight, and he was an indulged picky eater, as a child, as well as fed chocolate as 'a treat' by grandparents. Food is more than fuel for him.
The real bummer is that, whilst alcoholics can give up booze, we can't give up eating. Which puts into perspective the scale of achievement of people who have lost a great deal of weight and kept it off. They have mastered their addiction, and, whilst given up drinking is a great achievement, I don't imagine that too many recovering alcoholics could live with an 'you must drink, but only 2 pints a day' regime.
Any one who has never had a 'weight problem' can never know how hard it is lose it - and keep it off.
There endeth the first lesson !!!