The James Cameron directed film The Titanic
has a chilling tale about the possibility of Mr. Jack Dawson not actually being real. This is quite the opposite of the actual movie plot, where instead of a romantic love story, Jack Dawson is a figment of Rose's imagination.
The first time Jack meets Rose is when she is about to jump from the ship to avoid marrying her fiance. Jack appears in this moment as a protector. A protector from her subconscious mind to save her from jumping off the ship. Jack continuously tells Rose "If you don't break free, you're going to die." My thought on this is that Jack (Rose's subconscious) is attempting to tell her to break free from the restricted wealthy lifestyle that she actually hates and do as she pleases or she will kill herself.
There were no records of Jack ever being on the ship. The story is told that the ticket her possessed was won in a card game. Which would roll with the original story. But elderly rose comments later about the treasure hunters telling her "They never found anything on Jack", she replies "No, there wouldn't be, would there. ...He exists now only in my memory." This certainly goes along with the theory.
The tragic scene where Rose lets Jack drown. It has been proven time and time again that there was enough room for both Jack and Rose on the floating board. Rose was able to let Jack drown because one, he wasn't real and two, this was to represent her letting go.
Picture of the floating board