Proper workout, balanced diet, and adequate rest are the keywords for success in muscle building. I think it's a mix of the amount of effort it takes, the insufficient attention having powerful legs gets within our culture compared to the chest muscles plus they myth that exercising your legs will spread your body too thin and therefore stunt muscle growth in the "preferred" upper body. Then they are motivated to review their particular current diets and try to pinpoint where they are stacking around the weight and receiving their daily nutrients (or lackthereof). Most traditional muscle-building programs within the market won't work for naturally skinny guys. It's important to a muscle with a diet which is designed for muscle building.
After you get your diet and supplementation (if you choose) down, you need to figure out your training. Long sessions will always be nice in the wedding you truly want to muscle tissue up however you can also do shorter sessions that are far more intense.