David's original sin—the one that hurtles him toward every bad decision and shapes his interpretation of events—is vanity. As early as the book's first lines, David addresses this character flaw, applying it to all writers:

A writer never forgets the first time he accepted a few coins or a word of praise in exchange for a story. He will never forget the sweet poison of vanity in his blood [...]. A writer is condemned to remember that moment, because from then on he is doomed and his soul has a price (3).

David isn't alone in falling under the spell of his own perceived talents as a writer. When Cristina worries that Pedro will know David has rewritten his book, David says, "Never underestimate a writer's vanity, especially that of a mediocre writer" (98).

It's an open question whether writing makes people vain or vain people are naturally drawn to writing. Even before David becomes a writer, David sees much of himself in Pip, the protagonist of Great Expectations who aspires to rise up from the underclass. Unlike Pip, who finds a wealthy patron as a result of a kind deed, David obtains himself a benefactor out of sheer randomness.