Are you not gaining muscle mass? Have you figured out why? Well, the answer lies in your actions. Just read them and you will know ‘Why”. One of them is that you are missing out on the benefits you can reap from compound lifts. Second, you are not eating enough. This is one of the worst diet mistakes for gaining muscle. Third, you are not paying attention to your post workout nutrition. Fourth, you are not having calorie-dense snacks handy.
There are a few more reasons, for more details on them, go through the infographic below by GymJunkies.