There once was a man with a water pump. To a friend he said, "This water pump will provide you with all the water you need. Here, it is yours." The friend was delighted to receive it, since he was thirsty as well as needing water for his dying garden.
The next day the man came by again. His friend accused him, "This pump does not supply any water. You lied to me."
The man asked, "Did you plug the pump into power?"
"Plug it into power and you shall have all the water you need."
The next day the man came by again to see how his friend was doing. "You lied," his friend said. "I plugged it into power and it gave no water."
"Did you let a pipe into the well so that the pump could draw water?"
"Let a pipe down into the well and it will give you all the water you need."
The next day the man visited once more and again his friend said, "You lied; I still have no water."
"Did you prime the pump with water?"
"Prime the pump with water and you shall drink indeed."
The following day the man visited his friend and the friend rejoiced for all his water. The friend said, "Did I not tell you the truth?"
"Yes," said the man.
"Why then did you call me a liar?"
"That's how it seemed; I did not realize it was my own ignorance that made your word a lie to me."