Training dogs should be fun. When you lose your temper you lose. Overambitious dog owners, who expect miracles and don’t give anything in return are free to have a taster of how it feels when you haven’t got a clue what is expected from you and the less you understand the louder your teacher shouts: I can give them a language lesson, Icelandic, to make it properly ‘fun’, using grammar-translation and a cane. No praise, just punishment. And yes, I can shout, I just don’t shout at the dogs. I promise it will be boring, scary and you’ll learn nothing except how to despise me.
It really is easy. If you want your dog to learn, praise, if you want to be despised, punish.