Someone asked me, this morning, for advice on their dog. I listened to the issue. The dog was found on the side of the road and this person "rescued" it. Well, it turns out, this particular dog is fine with some people but will growl, snarl and bite the head off the next person. I, personally, have not met this dog but from what I'm told, it sounds fearful. Naturally, after being dumped on the side of the road. I asked if the dog was particular to men or women and the owner said no. I told the owner that it will take time for the dog to "come out of it's shell". The owner replied that she has had the dog for over a year. So that begs the question...HOW LONG will it take to train your dog?
There is NO clear cut answer! Your dog is ALWAYS learning, just like you. Just because you graduated high school and college, doesn't mean you stop learning. You learned how to drive a car or maybe a forklift or maybe you learned to dance or you've overcome a fear (for me it's flying, but there is NO way I'm getting on a plane anytime soon)!
Back to the fearful dog, I mentioned earlier, how long will it take for it to overcome this fear of people -- who knows? It could be a week, a month or even YEARS! Without having met this dog, I can't say why it's fearful, however, being left on the side of the road plays a HUGE factor. It could have been there for days, weeks or months. That would scare anyone!
Consistency, patience and time will be your best friends when doing any training. No matter if it's basic obedience or fear related.
Just because your dog isn't getting the command or overcoming something at the rate YOU'D like, doesn't mean he/she won't 'get it'. Give it time! Give it patience and be consistent!
Remember the phrase, this too shall pass! Trust me, it will!