The statement (1) "everything in moderation" contains the seeds of its own destruction.
"Everything" includes moderation. So to take everything in moderation implies that one should be moderate about moderation itself. To put it another way: (2) One should take everything in moderation, including moderation itself, and including the extent to which the next three words---everything in moderation---are understood, accepted and acted upon.
But now we fall into an infinite regression. Because statement (2) implies that one should be moderate about statement (2) itself. Which in turn means that (3) one should take everything in moderation including moderation itself, but only in some and not all instances (ie moderately), and that in other instances, one should be moderate about statement (2) itself. And then similarly for (3), (4), (5)... to infinity.
I now understand why "paradoxic" rhymes with "toxic". In fact, there is a very quick and simple resolution: instead of "everything in moderation", "most things in moderation".