A lot of people don't really know what they're doing when they go to the gym.  Because of this, they generally don't see results and wind up giving up after a few weeks.  When you get into weight lifting, there are a lot of things you'll need to learn.  In fact, I recommend that you do plenty of research before even picking up a dumbbell because you'll probably just be wasting your time botherwise.  

Since many ectomorphs don't really know what they're doing, I'm going to make a short muscle building guide that will teach you the basics of bodybuilding and how to best do it.  This guide is for the novice weight lifter that isn't sure if he's doing things right or isn't seeing results.  If you're not gaining muscle from working out, then you'e obviously doing something wrong.  In this guide, I'll be detailing possible reasons why this could be happening.

1. The number one reason why ectomorphs don't gain weight is because they don't eat enough food.  If you're eating under 3,000 calories a day, then you're definitely not getting enough food to gain mass.  Once you start working out your metabolism increases substantially, so much so that even a skinny guy can having a resting metabolism of about 2,500 calories a day.  In order to gain weight, though, you need to consume more calories than you burn.  That's why I say you need at least 3,000 calories, although you should be eating closer to 4,000.

2. Another common problem ectomorphs have is something called over training.  Over training occurs because you're running at a deficit or you're depleting your muscles over and over again before they have a chance to recover.  This can actually result in you losing mass.  You'll usually know if you're over training because you'll stop seeing gains and will become very tired and fatigued.  The best way to avoid this is to listen to your body: if you're too tired or exhausted to go to the gym, then don't.  If you feel like you need to eat more food, then do it.  These urges are your body's way of telling you that it needs something.  The only time you shouldn't give in to them is if you're trying to lose weight, for example.  In that case, you'd want feel hungry.

3. Poor quality of sleep: this goes hand-in-hand with over training, but is actually a very common reason why people don't gain weight.  Most of your muscle building is done while you're sleeping and your body is in rest mode.  You're not going to be repairing muscles while you're still using them, in general.  If you don't get a good night's sleep, then you're not going to build much muscle that night.  If you have trouble falling asleep, you should see a doctor and get help for it.  I've found that melatonin works great for me.