To be able to communicate with the animal, one must learn to "listen". The animals show us a lot about their body language and facial expressions. Everybody knows the wagging dog, but not every wag is joyful. It could also indicate excitement and tension. There are countless signals that the animals show. We must learn to understand them. The important thing is that we do not interpret and evaluate behaviour but simply observe it. Otherwise, we quickly end up humanizing the animals: "He has a guilty conscience." "He does it to annoy me." That's not how we do justice to the animals!
Dogs show very clearly whether they are afraid, happy or just stressed. It is important to recognize this and to react accordingly.
 
When you start a training session with your dog, start as if it were a new animal. Don't put your animal in a drawer "He can't do that anyway", "He won't listen to me anyway" or "That's no problem, he's been doing it right for so long". Observe the behaviour and consider how you can change or build it up with training. Observing and possibly changing but not evaluating and interpreting is the motto here.