Zuleikaa has a good point...there are examples in the medical literature of how, after many years of yoyo dieting, for example, the body enters an extreme mode where it stores fat, no matter what.
But I think ItsTheWooo has a point about Myth #3...at some point the person did overeat.
As a teenager I put on pounds from emotional eating; suddenly having a figure threw off my self image, there was stuff going on elsewhere, and I soothed myself with food instead of illegal drugs.
In my twenties I got a grip on the emotional eating, but I still went up and down...the range was 40-60 pounds, no higher, because I had learned some things, but not body chemistry.
When we all look back, we see a complex mix of what went wrong for us. However:
I feel our success at low carb means our previous difficulties probably have, at root, body chemistry issues.
Face it, we wouldn't have created such a problematical relationship with food, if the food we ate hadn't been such a problem!

Hear, Hear!!!