Though the ambiguous conclusion is part of what makes Casablanca such a remarkable film, not all of the ambiguity was intentional. During the filming, director Michael Curtiz and the writers could not agree on an ending. As Ingrid Bergman acted the part of Ilsa, she repeatedly asked for a clarification as to which man she truly loved, but no one gave her a straight answer. Bergman made the best of this frustrating situation by making this uncertainty fundamental to Ilsa's character. Ilsa is reunited twice with old lovers at the most inopportune times, and she has become shut off from her own feelings. The real choice at the conclusion is hers, but she elects to place it in Rick's hands. When she tells Rick to think for both of them, she absolves herself of having to take responsibility for her fate. Rather than take action, for which she would have to accept responsibility, she abandons herself to the whims of fortune. If Rick chooses wrongly, the fault will be his, not hers.

Bergman portrays Ilsa as stony-faced and almost cold, but Ilsa suffers most of all the principal characters. Although Ilsa gets a chance at both love and freedom in the end, she has not chosen her own fate. Her inability to steer her destiny is the result of her choice to let Rick decide, and in this decision, we see in her a dark, tragic fatalism. The romance of Casablanca is undeniable. The male characters are able to love completely and convincingly without appearing maudlin or sappy. Throughout the film Laszlo is an unapologetic optimist, and by the conclusion, Rick and Louis can envision brighter days ahead. Ilsa reveals herself to be a character of a different sort. Only in the final scenes do we even begin to grasp the full extent of her tremendous despair. Her dark fatalism makes Casablanca much more than a romantic tale set during a time when happy endings were not possible, and the fact that Bergman actually had to struggle to figure out who should be the object of Ilsa's true devotion renders Ilsa's despair and indecision all the more realistic and affective.