Sly Glutton:
I think a big part of my motivation is having control over my own destiny. I've wanted to gain weight my whole life, but there's always been some force opposing me. The pressures and expectations of family, authority figures, society in general. Even when I gained some independence, I only had that freedom with a physically demanding job. The first time I gained weight, it was like I was doing it for all the past iterations of myself. The skinny kid chugging milk in secret, unable to even guess that there might be other people like him. The scrawny teenager bewildered at his classmates complaining about getting fat in the off-season. The awkward freshman at university struggling to overeat while roommates packed on the pounds without even trying. I've worked hard enough to finally see the reading on the scale climbing higher and higher. Gaining how I want, when I want, is my reward for all that patience, determination, obsession, and occasional disaster.
I sometimes think of the times people around me have expressed disgust at fatness. I amuse myself at the thought of them pointing out that I've gained weight. As if I haven't noticed. As if I haven't treasured every bit of softness that I've earned. As if I should be worried that I'm somehow losing control of myself, rather than finally having total control over what I am and what I can become. It hasn't really happened to me yet (only family really notice or care, and they're very vague about their concern), but I often like to imagine the look on their faces when, having been told I'm getting fat, I smile patiently, as if they've stated the most obvious thing in the world, and say, “Yes. I know.”
So, I guess my motivation is becoming what I've always known myself to be. There's no escaping destiny! Plus, even if things don't go as planned, I get a few good experiences out of it.
Good for you man! I hope your journey goes well and you end up as big as you want to.