Part of the problem is a lack of established convention. When a theme park opens its gates in the morning, we expect a large crowd to jostle in through a constricted entrance like a funnel. However, when we queue up at the bank, if the line extends past the cordon, nobody runs up to that point and stands shoulder to shoulder with other patrons; we maintain a single file.

Which of these rules applies to cars merging? There isn't a set standard, so people invent their own and perceive their rule is universally understood.