IF YOU DON'T HAVE THIS... YOU ARE FINISHED 

Living without an essence of living is a waste. Life is not an end in itself. 
Life throws pieces (happiness, disappointment, heartbreak, joy, betrayal, success, failure...) at us, only purpose gathers these pieces and makes something meaningful out of it. Purpose is like a map leading us the right way to our destination. Purpose makes life meaningful.
NOTE: "people that don't have purpose determine their success by the success of other people".