like a dog chasing cars

Like a dog chasing cars means that the situation you are currently in is irrational because you wont know what to do once you get to where you think you are going. A dog chasing cars wont ever catch the car and if he ever caught the car, wouldnt know what to do with it. This phrase is used figuratively as a way to describe the fact that you should think twice about what you are chasing and what will happen if you finally catch it.