Valuable or unworthless of your pursuing?

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We are busy every day. Some one know what they want. Someone just do it. A dog of a farm often stayed on the side of road. He waited for car. When a car passed he ran after the car. He wana run faster than the car. One day the neighbour of the farmer asked,'Do you think your dog can run faster that the car.' the farmer answered,'I do not care whether he run faster than car. I care what's the meaning if he run faster than the car.' Sometimes we could meet some unworthless pursuing. However we can not see it clearly at the beginning.