Why are we interested in tracking down these regularities?
Not,
as a rule because we enjoy contemplating them for their own sake but because we are interested in prediction.
If we can rely on it that when we see a twister in the sky a tornado is approaching,
then if we see one we may be able to take precautions by finding shelter before it strikes.
If people who are in proximity to others who have colds get colds themselves,
we may keep Johnny from get ting a cold by keeping him temporarily away from Billy, who has a cold.