When I was younger I used to have the mentality that I had a "skinny brain" trapped in a "fat body" and that I had been punished with being fat forever because no matter how hard I tried I NEVER lost weight.
By "trying" I mean going into anorexic periods all throughout middle school and high school, because that's the only way I thought would help me lose.
This was before I knew anything about calorie counting, nutrients, or how my body really worked, or the fact that everybody loses weight differently and that everyone is overweight from different causes.
I've also been one with a lot of model-thin friends. The only few friends I had in high school who were fat were binge eaters, which I would not consider myself to be. (I ate normal and sometimes large portions of bad things and PCOS combo, but I don't really recall binge-eating.)
Back then I couldn't understand that or had never really read stories about binge-eaters and everything behind it, so I just thought those friends were the "typical fat girl" and because I wasn't a binge-eater I wasn't really a "fat" person.
This thinking was even worsened by all of the doctors and nutritionists that my parents took me to while growing up. We would tell the doctor or nutritionist that once I hit puberty I gained an extreme amount of weight around my stomach despite not changing my diet to go from "chubby" to morbidly obese in less than a year, I had terrible acne, hair growth, I felt exhausted all the time. (HELLO!!! Major sign of PCOS here!?!?)
Rather than checking my hormones and testing me, they would simply INSIST that I was basically stuffing my face with fast food all the time and that I only needed to change the way I was eating and "do sports".
I think these experiences also instilled that whole "I don't eat like the 'typical' fat person does, so I'm not really a fat person mentally, but I'm doomed to be a fat person physically forever."
This was some of the most aggravating, frustrating, and depressing times of my life and I'm glad that things are different now.
But the moral of the story is, despite thinking this way initially, I've come to realize that no one is really meant to be a "fat person" or a "skinny person".