"Turtles all the way down" is a jocular expression of the infinite regress problem in cosmology posed by the "unmoved mover" paradox. The metaphor in the anecdote represents a popular notion of the myth that Earth is actually flat and is supported on the back of a World Turtle, which itself is propped up by a chain of larger and larger turtles. Questioning what the final turtle might be standing on, the anecdote humorously concludes that it is "turtles all the way down".
I guess that's a good way to put it.
Ignore the science / reality / evidence and substitute your own opinion.
Must remember that one.
