Ask any politician who has been victorious in an election so close the votes had to be recounted.  ONE vote makes a difference.
Ask anybody who got the last of a certain blood type for a needed transfusion. One contributor made a difference. 
You make think that your actions do not matter in the larger scheme of things.  In truth, your ONE action might mean the difference between life and death to someone.  Stand up.  Be ONE who makes a difference.