“...[A] fool cannot be protected from his folly. If you attempt to do so, you will not only arouse his animosity but also you will be attempting to deprive him of whatever benefit he is capable of deriving from experience. Never attempt to teach a pig to sing; it wastes your time and annoys the pig.”

And never attempt to teach a liberal to think , it's impossible and a waste of time.

“Never attempt to teach a pig to sing; it wastes your time and annoys the pig.”  ;-)  Love it!!

It comes to mind with the pig analogy — it takes a good Republican to implement a failed Democrat's policy (socialistic insurance, 2nd plank of the communist manifesto, etc. for example).