I learned the same thing last year.
I spent way too much time in working at my computer last winter. I would work 12-16 hour days eating 1-2 meals. At 22 yrs old, I dropped down to the same weight I was when I was 15 (150). That's when I got my ass into gear and tried the Geek to Freak program laid out in The Four Hour Body.
Tim F says he was able to gain 34 lbs of lean muscle in 4 weeks working out ~4 hrs total. I did due diligence on the method and was actually able to go from 150 to 170+ within 4 weeks.
A couple things I learned:
• Most people put way too much emphasis on gym time and too little on nutrition. I would say nutrition is 80% of the work. Recovery time is extremely important for rapid growth too. • When trying to cram as many calories in a day as possible, a meal plan is a must. The more strict the better. • You can get better results curling a 10 lb dumbbell with proper technique than curling a 100 lb dumbbell with poor form. • For muscle growth, I prefer only 1 set of high weight with low reps (6 reps min, 12 reps max) • LOMAD (one liter of milk a day) is a lot easier than it sounds.