6'0 140 lbs

And I can honestly say that despite the fact that I am also thin as a rail, you are absolutely wrong. If you calculate how many calories you are eating each day, and keep an accurate journal of your calorie intake, if you maintain several hundred calories above your maintenance calorie intake, YOU WILL GAIN WEIGHT. Period. Genetics/naturally fast metabolism will result in a SLIGHTLY higher maintenance intake, but your body size is almost directly proportional to how much you are eating. If you eat more food consistently over a decent period of time, you will get bigger.

6'3" - 175lbs

It takes (roughly) 2500 calories for me to maintain my weight with the exercise I do. From what I have heard for any significant gain that means at least 3000 calories must be taken in per day. THAT IS SO MUCH FOOD. I don't have TIME to eat that much food, let alone the money!

I hit 175lbs like a brick wall.