Why are some people just born skinny?

It's not fair. It's easy to say that being thin doesn't mean they're happy; but think of all the extra time they would have to spend being happy, which other people spend being fat and melancholy. They would never have to diet, or do gruelling amounts of sit-ups, or work to be noticed- they're just beautiful. That may well be farcical- no-one would get a model body from eating; but it just so happens that there are plenty of regular people walking around who are just thin, and didn't do anything to get that way other than be born to the right parents.

The worst bit it, no matter how much someone like me tries, I'll never be thin. I'm just not genetically predisposed to it. I know it seems like all fat people probably say that, then secretly binge on chocolate cake when nobody's watching, but I swear I try. The last time I checked, trying does not entail eating.