In ancient Greece, Socrates was reputed to hold knowledge in the highest esteem.
One day an acquaintance met the great philosopher and said, "Socrates, do you know what I just heard about your friend?"
"Hold on a minute," Socrates replied. "Before telling me anything I'd like you to pass a little test. It's called the Triple Filter Test."
"That's right," Socrates continued. "Before you talk to me about my friend, it might be a good idea to take a moment and 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 absolutely true?"
"No," the man said, "I actually 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 friend something good?"
"No, on the contrary..."
"So," Socrates continued, "you want to tell me something bad about him, but you're not certain it's true. You may still pass the test though, because there's one filter left: the filter of Usefulness. Is what you want to tell me about my friend 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?"
This is why Socrates was a great philosopher and held in such high esteem. It also explains why he never found out that his best friend was having a secret affair with his wife. Source
