Sparta's joyful unreserved nature arises from the fact that she has never known anyway of living other than what she has now. I expect Stoic spent his first few years in a household with a lot of negative reinforcement. While it has it's place, too much can quickly damage a dog's spirit.
Can a pack have a culture? I think it can. I know it can when you add a human to the mix. I set the tone for what we do and what we don't. The other dogs reinforce that culture.
It was a simple river crossing. I'm glad to say as we headed back to the car, Stoic jumped it without needing a single word of encouragement. Its just what we do.