Once upon a time, there an old man selling anti-flee drugs on the street. He said his drug kills all the flees, and if it doesn’t work, he will give the money back.
A man bought the drug and went home. Days later, he came back angrily to the old man and said the drug doesn’t work at all and the flees are still flourishing.
The old man said lazily: “It is because you are not using my drug correctly.”
“Then what’s the correct way?”
“You should open the mouth of the flee and feed it a small spoon of my drug.”
The young man was furious and said, “If I have already catch the flee, why can’t I simply squash it?”
“I didn’t say you can’t do that.”, said the old man.