Never try to teach a pig to sing; it wastes your time and only annoys the pig.
Until this morning I did not know with confidence the author of that quote. My good friend and former colleague had rendered it on a simple piece of paper and affixed it to his office door with clear tape. For years it remained there. Over time, as Managers traipsed the carpeted hallway outside his office, parading from one meeting to the next, it became increasingly difficult for them to unsee this aphorism. Eventually, some of them became suspicious of who or what the target of this supposedly witty saying was intended to be – “Is he saying we are the pigs?” As you might imagine, eventually their suspicion gave way to annoyance. The piece of paper with the saying on it was deemed inappropriate by Management. He was commanded to remove it from his office door. My friend complied alright, he relocated the paper with the saying on it to an interior wall in his office. And with that its timeless relevance was revealed. Q.E.D. as they say.