Turtles All the Way Down
Infinite Regress · Unmoved Mover
An expression of the problem of needing something to explain something to explain something, etc., where the expression alludes to the mythological idea of a World Turtle that supports the earth on its back, and then the question being asked of what supports *that* turtle.
EverydayConcepts.io
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Origin
The origins of this expression date back at least as far 1838 and likely much further.