Not quite a quote, but a good proverb.
In ancient Greece (469 - 399 BC) Socrates was widely lauded for his wisdom. One day the great philosopher came upon an acquaintance who ran up to him excitedly and said
"Socrates, do you know what I just heard about one of your students?"
"Wait a moment," Socrates replied. "Before you tell me I'd like you to pass a little test. It's called the Triple Filter Test."
"Triple filter?"
"That's right," Socrates continued. "Before you talk to me about my student let's take a moment to filter what you're going to say. The first filter is Truth. Have you made absolutely sure that what you are about to tell me is true?"
"No," the man said, "actually I just heard about it and..."
"All right," said Socrates. "So you don't really know if it's true or not. Now let's try the second filter, the filter of Goodness. Is what you are about to tell me about my student something good?"
"No, on the contrary..."
"So," Socrates continued, "you want to tell me something bad about him, even though you're not certain it's true?"
The man shrugged, a little embarrassed.
Socrates continued. "You may still pass the test though, because there is a third filter - the filter of Usefulness. Is what you want to tell me about my student going to be useful to me?"
"No, not really"
"Well," concluded Socrates, "if what you want to tell me is neither true nor Good nor even useful, why tell it to me at all?"
The man was defeated and ashamed.
