One of the most common mistakes I see with dogs is the confusion of 'intelligence' with 'obedience'. I'm pretty sure that sometime in their lifespan you saw your dog in a sitting position, therefore they know HOW, they just saw no reason to do it when you gave the command.
GPs are not bred to work with humans, therefore they have no desire to please or for the most parts NEED h umans. That is what makes them able to do their jobs. Other breeds need to have their human pack to be happy. Give a LGD a couple sheep or goats and the whole human race can go extinct for all they care.
Dogs like that see no reason to do things just because some human said so. But give them a problem to solve and they will amaze you with their intelligence. They can be very obedient if you have something they want,of course.
GSDSare an opposite example. Super intelligent problem solvers AND people-pleasers. They are meant to work hand-in-paw with their owner. Labs and similar dogs I've found to be the other way around. Eager to please, but not great problem solvers. They can be very precise in their obedience because they don't sit around thinking of new ways to do things. To them, sit means put my butt on the ground, doesn't matter if its the first time or the 10,000th time. More intelligent breeds try the sit in 1000 different ways. "What will happen if..." seems to be their training motto.
Last night my dog was 3 steps ahead of me all night. We were working on recalls and fronts. Usually that is followed by me putting him in heel position. So, he decided to skip the middle step -slid into a sit at my feet and popped back up and into heel position without waiting for the command. I took a step back and called him to front again. "ah!" He thought, slidding into a sit, bouncing back up and went around me into the heel position. Tried the exercise again. He pondered a second, came into a front and then did a down. He knew that we never stop at "front" so he was trying to anticipate the next move.