Difficult Puzzle

A man was walking down a street when he sees a blonde couple who looked extremely happy. He goes up to them and asks: "Why are you guys so happy?" The couple says "We just finished a puzzle that took us 3 years!" "3 years!" the man said "It doesn't take that long to do a puzzle." "Oh yes it does" said the couple "It said so right on the side of the box 2 to 3 years...!"