Are you frequently punishing your dog on training? Is your dog more aloof around people of most often stays away from people? In training your dog, you might be thinking that you are doing the right thing and that includes punishing your dog. Did it not occur to you that maybe it is more easier to teach your dog the rules or to teach him what you want him to do and reward him than to punish him by not obeying you?
Punishing your dog can mean a lot of things. Read here and know the effects of punishing your dog and what to do about it.