亡羊补牢

One morning, a man found that one of his sheep was missing from the pen.
“Where has it gone?” He was puzzled.After checking the pen carefully, he found a hole in the wall of the pen.A wolf had broken into the pen and eaten the sheep!
“Well," he said, “the wolf has taken one of my sheep."
So he walked away sadly and went to tell his neighbour.The man's neighbour said,“You had better fix the hole quickly."
The man said,“The sheep has already been taken. What is the use of fixing the hole?"
Then the next morning, when he went to check his sheep, he found that another sheep was missing. The wolf had come back and eaten a sheep again!
Now the man understood that his neighbour was right.
Immediately, he fixed the hole.From then on no more sheep were taken by the wolf.