I've always had a thing for catchy sayings of two different related kinds, which are almost mirror images of each other.
The first kind of saying is the paradox that seems plausible at first reading, but becomes apparently contradictory after you think about it. For example,
As everyone knows, Truth is absolutely subjective.
James Taranto gave us a lower brow example when he wrote, "This isn't an ad hominem attack, you jerk."
And William F. Buckley, Jr., crafted the famous insult,
I would like to take you seriously, but to do so would affront your intelligence.
The second kind of saying I have in mind seems meaningful at first reading, but is actually just a tautology or truism. When I was a kid my dad would brag to us about how fat his wallet was by saying,
I've got so much money, I've got money I ain't even spent yet!
Another example is, "If you don't improve, you'll never get any better."
I'd love to compile a list of similar sayings. Do you have any others?