I have seen many people in the gym workout for 3-4 months and see very little results and then give up. If they would only educate themselves on what it takes to learn how to gain muscle then they would realize that working out is only one part of the equation. Your diet is the biggest factor that will determine if you build muscle or not.
Think of a top fuel dragster without fuel. It wouldn't be very fast would it. Same thing with your body. If you don't feed it what it needs to repair itself after each workout then your not going to get anywhere. So pay close attention to your diet.