When you adopt a dog, you know they come with a history. She may have had no human contact until she was rescued, or maybe the only contact was abusive. Dogs with histories like this can be unresponsive to training, which frustrates their new owners and result in a return trip to the shelter.
If something like this happens, it’s usually because we humans have forgotten that the dog we are trying to train may not even understand the concept—they don’t know how to learn.
From: theilovedogssite.com