This is why reading a dog is imperative.
Things like age, factor into emotional maturity.
Self confidence in dealing with humans, has a huge impact on how much pressure THIS DOG CAN TAKE TODAY! Tomorrow may be totally different with this dog.
More passive breeds can handle much less pressure, when compared to other breeds.
The size of the dog factors in. It is hard not to look like Godzilla, when agitating a Chihuahua. The lower visual profile you show to a dog, the more emotional pressure you can put on him.(all fours, or maybe even laying on your belly)
The ONLY way to know these things, is by asking the dog. This is all happening in a fluid and dynamic time frame. You must be able to read while in motion.
I hope you have noticed that the only trait required, is that they are a dog. A timid breed of dog can still be taught, it just takes a lot more tiny steps, than other breeds.
You have to decide if it is worth your time to train your 5 pound wimp, for man work.
When I was a kid, I taught my Mother's 2 pound, 4 ounce adult male Poodle to viciously attack on command. He put on one hell of a show, but could really only ruin your socks.
No matter the size or breed, they all are genetically disposed to protect the pack.
E-Dog - 2012 WPBTCA National Championships
The time when screech owls and Bandogges howl and spirits walk and ghosts break up their graves.
Act I, Scene IV of William Shakespeare's "King Henry VI"