Ancient boxplots
When we learn things, we tend to get the impression that the things we learn have been passed down to us from the ancients. We think that the ways of thinking and doing we are presented with are the only way to think and do, and they were decreed by some all-knowing prophet in prehistorical time.
This can cause some problems if you happen to be one of the people who does not naturally think and do in the ways you are shown. You can feel a bit stupid because you can't understand the only legitimate way of understanding, which people seem to have understood since time immemorial.
But of course, it's just not true that the things we learn have always been known.
This was brought home to me very clearly the other day when I learned that the boxplot was only invented in 1977. 1977! That means that when I first learned about them, they had only been in existence for twenty years!
In some disciplines, the students get the impression that boxplots are the most natural and best possible choice for displaying numerical data, as decreed by the ancients. (To be fair, they are not told this explicitly, it's just the impression they get.) Yet boxplots are not actually all that easy to understand for a lot of people because there's quite a bit of abstraction between the data itself and the boxplot. If you as a student can't understand this "most natural" way to display data, you can feel a bit like you're stupid and have no hope to ever learn statistics.
But they were only invented in 1977! No-one before that time thought they were the most natural way to display data or they would have been invented earlier. Even Tukey himself only created them because he thought they could clearly show very particular aspects of the data. You can't feel stupid for not understanding something that no-one thought of until quite recently!