I bought a total of three pug pups from unrelated breeders over the years and they were all easy-peasy to train. They differed in intelligence, but none of them were rebellious or defiant.
Then I got a fourth one from a different breeder. This one was young, about a year old, but she was a show dog whose career didn’t take off, and had been raised in kennels. I could not train her to save my life. She ripped up the furniture and ate the trash, could not be housebroken, would not learn to sit or stay, and howled miserably all night long. This last was puzzling, because she was kept in the family room with the other three pugs and had company, but the screaming and howling still went on.
I kept at the training for several months but it was no good. She had learned absolutely nothing. I finally returned her to the breeder and went home deflated. Like Aspenglow, I thought I was pretty good at training dogs, but Terry Lou took the wind right out of my sails.
Later I learned that dogs raised solely in kennels for their first year are very hard to train, having not been socialized with people at a key age.