They Always Think They are Wrong

I have many students that do this. They go to turn in their tests in a folder at the front of the room and as they are turning it in they check their answers with the person who turned theirs in before them. No one is cheating here they know once they open that folder that their test is over, and I would prefer that they didn't do this but when I'm more worried about cheating I don't always notice it. The interesting thing is they ALWAYS assume that if they got a different answer from the person who turned it in before them then they MUST be wrong. They use this assumption whether the person right before them is the smartest person in the class or not. Where did they get this idea? How do they know there aren't different test versions out there? WHy don't they trust their own work?