After a few years of marriage, it came to light that my wife thought the earth was flat. It wasn't some religious thing or cult thing, she had no affiliations. She just came to that conclusion based on visual cues in the world (like ground looks flat) and believed it without it ever being challenged in it.

It came up when she mentioned that a plane fkying near the sun must be getting hot, and I'm like Whaa? I explained the sun is so far outside the earth that that plane isn't feeling much different than us. She revealed she though the sun was inside the earth (like we lived in a snow globe on a flat planar surface) and the sun just went down behind the mountains at night like half hour away.

I was stunned. We had a 4hour talk about the earth as a planet and the solar system and how gravity works.

She curled up in a fetal position and had an existental crisis for the rest of the day.

Somehow she missed school for the gravity, solar system etc. And I'd destroyed her entire core belief system; that she had developed herself.