Your body language, tone, attitudes, moods and feelings can destroy your dog's training.
Why? It's simple. Your dog's first language is non verbal communication (body language). The saying "actions speak louder than words" is true.
A human example would be the phrase "I'll talk to you later". If it's said one way then it means simply what it says. Said another way with a glare, a low tone of voice, and a clenched jaw or fist then it means something entirely different. (I'll talk to you later and you're not going to like it)
It's true. It's true. (Let's apply this.)
Your dog has run off down the street and is inspecting the neighboor's lawn. Your calls fall upon deaf ears. Finally your dog decideds to meader back to you. You say "good boy" (or girl) pat him briskly on the head. You think you're doing good because you didn't punish him when he came back. (training dog to return)
You've just wasted a great learning opportunity for your hairer friend. (your dog)
Your dog knows your mad. Your dog probably even knows that he was being bad. It may have been worth it for that chance of freedom. So the wasted opportunity is the giant chance to reward, and enforce a concept to your dog. The concept is " if I come when Mommy or Daddy calls me, good things happen". Make the reunion a happy occasion. Remember that you love your dog. Baby talk, scratch and play with your dog.
A trainer once told me said " However long it takes your dog to do something, you reward them at least that long".
You've had a horrible day. But holding to your training schedule you trudge to your dog to work on the latest trick or concept. You withold your duty. That's good right?
Wrong. Wrong. Wrong. Your dog is like a mirror. If you are excited your dog is excited. If you are scared your dog is scared. Sometimes your dog will pick up on feelings you weren't even aware you had. In this case you would have been better off to include your dog in something relaxing. Let your dog sympathize until you feel better. You catch your dog in the act of something bad, but very cute. Or very funny. You laugh and say "no no"
You've just devalued the word NO.
Your smiles are reward enough for most dogs. And dogs don't really understand exceptions or special circumstances. So sometimes its important to feign anger. Heavy footsteps are often enough to intimidate a naughty pupppy.