Just because there are cases where it does work didn't mean it works for everyone, there are more then a few well know well supervised cases which show that it don't work on all cases. Especially not long term.
Yes, what I can say it will be harder for some persons than others. The hormonal environment in the body can not be disregarded and can be either disrupted or genetically different. STILL, restricting your eating habit (caloric deficit), will.always.work.