Why are our beliefs so enduring, even after we see that they may be false? In his book The Believing Brain, American psychologist Michael Shermer provides some valuable answers: we are more receptive to arguments that confirm our beliefs than the ones that challenge them, and we are very good at justifying our inconsistencies and believing what suits us best.
As Shermer sees it, we are also naturally gullible and open to false beliefs. Myths, religions, and magic have been used for millennia to explain reality, whereas the scientific method is only a few hundred years old. Anecdotes and old wives' tales come to mind easily, while applying science requires effort and more in-depth knowledge. Our brain is more comfortable with intuitions and emotions than with sound research based on hard evidence.
Beliefs also bring people together. Sharing a belief makes it possible to form a group and create bonds of solidarity. Birds of a feather flock together: we think the same, so we unite. This is perhaps particularly striking when it comes to religion, but this phenomenon can be seen across all social institutions. A quick browse through the discussion forums of sports team supporters, environmental activists, or moms advocating for breastfeeding will likely be enough to convince you. Which is also the reason why I found it difficult to wean myself off my own false beliefs about milk; doing so somehow made me a traitor to my Québécois identity and the community I belonged to. The liter of milk sits proudly on the checkered tablecloths of our sugar shacks.* This is what we leave out for Santa, to encourage him to take a break between chimneys. This is the treat we give children when they come home from school. It is also the cheese platter we enjoy at dinner parties with friends. In short, by giving up my false beliefs about milk, I was betraying my farmer grandfather, my mother's cooking, and my friends' warm generosity. And last but not least, I was betraying Mr. Sealtest, too.