The director, Michel Gondry, alludes to relationship struggles, by stitching together a not so spotless tale of the mind searching for love and ultimately eternal happiness. Clementine is telling Joel a story from her childhood, and as she tells the story.
Looking at the happier moments of love with Clementine stemming from the relationship that they had initially, Joel struggled to reserve at least some of her memory and the love he has for her. Joel takes a big step at the end of the film by running after Clementine when she leaves.
She does not care what anyone else thinks, and that is part of what Joel once loved about her - even though her erratic tendencies are also part of what drove them apart. His motivated action indicates that Joel has grown, and perhaps he will be able to be more open if he and Clementine reunite.
Clementine leads Joel into the house, so clearly she is the more brazen of the two. It engages the audience and they cannot wait to see how things unfold.
The compelling story begins when emotionally reserved Joel is headed to work in New York City one morning when he feels an incomprehensible compulsion to call off from his job and get on a train to Montauk, Long Island