For a while, we assumed that the stars were gods, watching over us. Currently, we have a better understanding of the physical nature of stars.
For a while, we were drilling holes in people’s heads or cutting out parts of their brains in order to make them “normal” again. We know better now.
For a while, lesser status was given to certain human beings based on superficial attributes, like skin color. Some of us still feel the pain of that stupidity.
For a while, some people were stupid enough to think that a style of music could bring down the whole of society. Okay, some people are still that dumb.
The point remains: we think we know stuff.