The question is a deceptively simple one, for reasons upon which I will elaborate. Firstly, people use umbrellas for the purposes of remaining dry, or not wet, specifically when their surrounding area is being rained on - pelted with wetness, as it were. But whence this desire for retaining dryness when one's environment is wet? Whence this human urge to ostracize oneself from the natural cycle - or rather, to ostracize nature from one's own life? Is the clue not in the question?