J.M. Blakely was an elite bench press competitor. In addition to his pressing power, he was famous for his ability to manipulate his weight to make or change weight classes. Here's what he had to say about gaining weight (from his article The Big Boy's Menu Plan - Powerlifting USA):
I am reminded of the time I was complaining to a friend about how hard I was trying to get my weight up to 300 pounds and how tough it was for me to eat so much, and boo-hoo-hoo. The friend looked at me, clearly fed up with my whining, and remarked "I see several people over 300 lbs at work (he was a physical therapist) and they really don't seem to be trying all that hard! They weigh 300 and they don't try!"
This put it in better perspective for me. I even had the advantage of working out with weights to help boost my weight and these guys were out eating me and my best effort without so much as a second thought. If people can do it on accident, I could certainly do it on purpose! And I did. So can you.