I am really fascinated by this thread. I can totally relate to what Timefor said and I could have written this word for word about myself:
My personal story: I've been obese and I've been a healthy weight. But mostly I've spent my adult life in between, as an overweight, slightly portly, if still curvy, woman. I've rarely managed to maintain a healthy weight for more than a year at a time. However, in terms of the principles I've learned through the past decade it goes something like this when I'm slim(ish!):
I have no gears, no brakes, no natural mental stopping point - I am either on point, or I'm not. And when I'm not, I mean I'm really not! For example, I cannot snack in a controlled manner. I just can't. It is the highway to hell for me. Therefore I do best when I commit to a fairly samey eating plan, because it removes the element of too much choice. So my breakfast and lunch are almost always the same, six or even seven days a week. I love to cook though, so I satisfy that creative culinary urge through our evening meals.
I am a phenomenal emotional eater. Food has been my solace, my reward, my joy, my guilt, my self punishment even, for my entire adult life. And in combination with the above lack of self discipline, I simply cannot have snack/treat/'bad' etc foods in the house, because the urge to eat when I'm in any kind of emotional state is overwhelming. Utterly overwhelming.
But what is so interesting is that AmericasTorturedBrow then said this, which means she has basically the same mental relationship with food as I do, and as Timefor does, and yet she's very slim. 
I'm 5'9" and bounce a few pounds either side of 135lbs (9.7stone) and size 8-10
I have a horrible relationship with food, really relate to PP who says they use food as every emotional response - joy, sadness, pain, boredom, punishment. I have no off switch when I'm in a bad food phase and will eat to well beyond full, go to bed with a painful stomach etc…….I am not sure why I am not fatter….
I am only 5' 2" and I DREAM of being 9 stone 7 lbs again, it is my ultimate goal, and I could never in a million years imagine weighing less than that. I think my body type and my metabolism are such that, knowing how hard I have had to work in the past to lose any significant amount of weight, the only way I'd ever weigh under 9.7 would be if I developed some kind of eating disorder and exercised obsessively to an insanely unbalanced degree.
It's funny to think the weight I would love to be (at 5' 2") would make me deliriously happy and I'd feel like the bee's knees, I'd still be curvy and a little plump but I'd look and feel normal, be able to wear pretty much what I liked and I'd feel slim, healthy and happy, yet I know many lifelong skinnies would be suicidal at the thought of being that fat.