My favorite example of need vs. want is Flight. What makes that movie interesting is that it uses the standard protagonist-overcoming-adversity-to-achieve-the-goal, which means the audience is (or thinks it is) rooting for the protagonist to succeed. But what the protag needs to do is to fail, which means being honest and changing the behavior that has allowed him to triumph in previous situations even when doing so worked against his movement from disunity to unity. The movie makes this point by playing "Sympathy for the Devil" when the John Goodman character enters to help the Denzel Washington protagonist "win" his case.