While I'm out walking my dogs I often run into people who are shouting verbal cues at their dog. They are in panic mode trying anything they can to get their dog to perform some sort of behavior. Some of the more popular shoutings are heel, stay, leave it and come. When I do a photo shoot many people will tell their dog to stay. Then I ask them if their dog knows what stay means. They look at me strangely and then answer no. Isn't it funny then that they keep yelling the command at the dog, hoping somehow that the dog will get the idea. Hmmmmm?
It doesn't work this way; you must teach, then practice, then proof and then train and train and train some more. Dogs do not come with a built in knowledge of these words. Although it may seem that they should; just like the names Fido and Rover, the words sit,come and stay seem to go with dogs. But unless you take the time to teach your dog what these words mean, then they mean nothing to your dog, no matter how many times you say them.
If you have taken the time to teach your dog some of these words and still they don't seem to work, then you still need work. And all those sit, sit, sit verbal cues that your yelling at your dog are undoing any training that you have accomplished. What you are now teaching your dog is that "sit" means nothing. It may also be creating a negative association to the word as well, because of your state. In this state you are probably growing angry and your dog knows it.
When you start educating your dog you need to do it in a quiet area with no distractions. You teach them until they are consistently performing the behavior. Then you add a tiny distraction, say someone walking through the room. Next you would practice in different rooms and then as your dog succeeds you build the distractions. Never expect your dog to perform in an area of high distraction if you have not trained them to do so in a high distraction area.
If you find yourself in a situation that is stressful and you know that your dog is not going to be able to be successful in what you ask, then don't ask. Don't use your verbal cue if you are not going to follow through. Make a mental note, more training in high distraction areas. Lots more training, you cannot expect your dog to do their job if you have not done yours.