The most accurate comparison between how a fairy tale and a memoir express theme would be:
The fairy tale would rely mostly on plot to express theme, and the memoir would emphasize the significance of real-life events.
Fairy tales typically use plot-driven narratives with fantastical elements and moral lessons that often emerge from the events within the story. The structure and events are central to conveying themes such as good versus evil, perseverance, or the consequences of one's actions.
On the other hand, memoirs are grounded in personal experiences and seek to convey deeper meanings through reflection on real-life events. The significance of those experiences, memories, and the lessons learned from them are key elements in expressing themes in memoirs.