One Piece's Luffy has another dream apart from being the Pirate King and it seems the Elbaf Arc has indirectly revealed it.

a pirate who was locked away on Level 6 of Impel Down but escaped during Luffy's invasion to save Ace, in order to lure Hancock to him and use her as a hostage against the World Government due to ...

Ace, Whitebeard is killed while fighting ... wildly and painfully. In this moment, Luffy believes his crew could all be dead because of his actions, and he does not know how he can go on.