When you are very young, you don't learn about the greater world primarily by experience: you learn by being told. Things like "don't cross the street without looking both ways" and "you have to eat vegetables to be healthy" and "brush your teeth so that they don't rot" aren't things we can learn by experience, either because it would be too dangerous, or because it would take too long and involve too rigorous or too costly an experiment. So we trust the adults in our lives to tell us how the world works, and the ways we should behave in order to be safe.
Unfortunately most adults don't know the answer to questions of how the world works, so they just repeat what they have heard, or say what makes sense to them. This can result in a lot of mistaken beliefs that are very deeply embedded in our minds.
I was in my 30s when I first realized that my parents were either mistaken or dishonest when they told me that if I ate too many spicy foods it would burn out my taste buds and I wouldn't be able to enjoy spicy foods any more. Looking back I can imagine that they thought this was an actual possibility, or they simply didn't want me to eat up all the salsa and pickled jalapenos in the house (which I would have since those are on the short list of foods I like). But I spent three decades limiting the amount of heat-spice in the foods I ate so that I would not "burn out" my taste buds, and it wasn't until I mentioned it out loud to someone that I realized that it didn't make sense.
In a more sinister example, when I was 11 years old I was in the "overweight" category for my age and height and a doctor told me that there is a valve at the bottom of your stomach that will not open until it has been 5.5 hours since you last ate, and if you eat too often the food automatically gets stored as fat. So I carefully made sure to wait at least 5.5 hours between meals, for years. I never questioned it because I trusted that adult to have good information and tell me the truth; it became a part of the facts of my life and I didn't even look at that belief for decades. I was acting on it as if it were true, and it was not.
I think she was trying to trick me into eating less, imagining that I must snack too often and thus have become fat due to overeating. Eating too much was never an issue I had because I don't enjoy eating, generally, and have to push myself to eat. I now know that this fucked up my metabolism and I am pretty sure it is the reason that I am at least 6 inches shorter than either of my siblings.
When I was a kid, it wasn't possible for me to fact-check my parents or my doctor with the internet. The closest thing to that would have been the set of encyclopedias my parents bought when I was in my mid-teens, and though they might have been able to prove that there was no magical time-sensitive valve at the bottom of your stomach, they wouldn't have had information about the long-term effects of eating peppery foods.
More to the point, it never occurred to me to question these authorities because I had no other experts to turn to. Now, almost anyone can find expert knowledge on any subject if they can read and have access to the internet. It has become easy for literate people with internet to resist superstition and other false claims, if they are inclined to do so.
In the past decade, the availability of the internet has driven a decrease in the percentage of people who believe in "fan death." I hope and imagine that youth growing up with access to the internet will develop habits of fact-checking early on, and will be less vulnerable to believing in false statements merely because they have been uttered by an authority. I also hope that parents will respond to questions about topics on which they are not an expert by saying "let's look it up" and in this way, childish curiosity can lead to better education for their parents as well.