Something that makes me sad, that I hear all too often, is "my dog is dumb," or "my dog isn't smart enough to learn that" --- I don't believe that any dog is dumb. If a dog struggles to learn something in a particular way, we need to adjust the way we are teaching it to suit them. If they don't make any progress at all* in a session then we may need to rethink. Just because something has worked for the fifty other dogs you have trained, it doesn't mean it is the only way of teaching it, and just like us, different dogs learn in different ways. For some, we need to show them how to do a behaviour, through luring. For others, putting an object in front of them and shaping a behaviour will suffice. Some dogs need us to change our positioning to help aid progress. Some dogs need us to change the set-up of the environment to succeed.
Plus, the more you teach a dog, the more they can learn. Because they need to learn how to learn. A five-year-old dog with no prior training is likely to take longer to 'get' a behaviour than its five-year-old sibling who has been doing tricks for their whole life. And some dogs just take a little longer to understand training criteria, then it suddenly clicks and they never perform it incorrectly again in their lives. So just because your dog is not able to fully comprehend how to do something as quickly as another dog, it doesn't mean it is unintelligent by any means.
*Another thing that I have noticed is that dogs do in fact make progress, but often it is so subtle, or not rapid enough, so owners don't see it. We sometimes expect visible results in one session, and when it doesn't happen we become frustrated and think the dog isn't getting it. Second session, again, it seems like no progress was made, so we feel close to giving up. Then, in the third or forth session, suddenly the dog appears to get it. The dog has actually been making progress, but because it has happened a little slower we haven't appreciated it. This is why filming training sessions is such a good idea, because you can probably spot very obvious differences between the beginning and end of the sessions that you couldn't when it was occurring.
An example of this is "my dog won't roll over." This is such a common one. Because we expect a full roll over in one session, but for many dogs this is totally out of the question. So we need to look for small successes. Every training session that ends with a slight weight shift when you lure them is an absolute win! And then, when you least expect it, your dog will follow the lure all of the way around, after a few sessions of seemingly negligible yet actually immensely valuable training.
We have to remember that if we set our dogs up to succeed, we recognise progress and we celebrate even the smallest of wins, training becomes a whole lot more fun... and I guarantee your dog will hugely exceed your expectations!