It’s interesting that you’ve seen a wide range of answers here for a relatively simple question, right?
I think it shows there’s two ways people gain the ability to keep confidences or show integrity.
1) They feel the importance of integrity deeply (or are told of its importance) and never need to question it. Integrity is part of their basic makeup and who they are. It’s just right. No further explanation needed.
2) They’ve thought about themselves (or the the world) without integrity and decided it’s important to them. It might be that they acted without integrity and didn’t like the results, or they witnessed someone else and didn’t like it there. But somehow they came to where they are through experience.
My wife is in the first camp. She just knows what feels right and there’s not much more to worry about. She does the right thing because it’s the right thing.
I’m more of the second camp, I have to think it through. I’ve screwed up more, and had to apologize more. I do the right thing because I’ve decided I don’t like where the wrong thing leads and who I end up being.
You could take a broader look and probably find a lot of correlation between people’s beliefs on integrity and other behaviors and interests. I would imagine the majority of those drawn to areas where confidentiality is important value those traits highly themselves.