Ducks-Are-Fish Realization

If there is something you thought for a long time, and finally realized it is different, then it is a ducks-are-fish realization.
This comes from the time when I thought ducks and chickens were the same animal, and when I found out they were different, I immediately had the assumption that ducks were not birds. And when someone asked me, I responded "I think they're fish."

name just came to the ducks-are-fish realization that tortillas are not made with bread, but instead derived from wheat or corn.