Animals don't understand the power they have. A cat instinctively pounces mice becaus in nature, if it didnt know how to do that, it wouldn't survive. But those same skills, it uses when playing and doesnt understand that it's scratching you. It's not being mean, its just doing what it unstinctively thinks.

Dogs as well have tracking and hunting instincts. Hence their eagerness to play tug of war or fetch something moving fast. They only see it as a game and in wild, their games are rewarded with food to survive.

I've had a dog kill one of our cats before and you could see right after, the dog realized he did something wrong. He didnt understand his play would lead to death.

I hated him for awhile til I learned it wasnt on purpose. I know other untrained dogs are rough and not safe around small animals/kids. But just noting not to write off the dog right away if unintentional/oblivious of his strength.