I am same as nijinsky I am a size 6/8 and its easy to stay this way as I dont know how to cook that many things. My dad is a chef and 'he always says you should never trust a skinny chef' He has lived with that mantra all his life and is the only one in my whole family that is overweight or anywhere close. He has slimmed down a lot now but he still finds it a struggle I think. I find it difficult to imagine that mindset cause I just think dont eat too much as its easy for me, my brother and my mum.
From what I have noticed overweight people are usually pickers. My dad and friends say I have only had but then you see them sneaking stuff from the fridge/cupboard and foraging through the day. Another thing I see is them making a big deal about having a salad/something healthy then saying I only had that for lunch and you had a maccy ds why are you skinny? When you think well yeah but I have had no more snacks and you have had a couple of biscuits, bit of cheese, crackers, bite of this/bit of that.
Portion size is another biggy and even though some overweight people do exercise a lot I know move quite slow through the day. its surprising how much you lose/maintain weight by just moving fast all the way through the day zipping from here to there. I think if some people I know doubled their speed walking they would lose a lot more weight. If you do that a lot then less gym would be needed, which is important for people who hate the gym. Obviously hard to do this if you have an office based job though, but even running up the stairs, zipping round the office makes a difference imo.
Cars are another reason I think its harder to lose weight. Taking the car a teeny distance to the shop and thinks like that. Its easy to do but it makes a lot of difference. I have seen a lot of people put on loads of weight after becoming car drivers.
I also agree with olifin about portion size I never worry about weight it just is that naturally I would only eat a childs portion size.
Easy for me to say as slim I suppose but these are my observations. Realise its harder in practice because I would feel sick if eating through that 'full' feeling whereas for larger people they would feel the same struggle ignoring the constant hunger.
I do think however just things like not always taking the car, moving faster etc could make a difference to people I know who want to lose weight, and by doing this they wouldnt have the 'dread' of the gym or waste money on so many fads. Fads wont ever work and companies prey on this with their gimmicks and thats why its such a lucrative industry.