What did Reynie suddenly realize about Mr. Curtain's weakness?

Reynie’s realization about Mr. Curtain’s weakness being related to his anger is crucial to understanding the antagonist's character. In the context of the story, it is revealed that Mr. Curtain has a unique condition that causes him to fall into a sort of trance when he becomes extremely angry, which is referred to as "narcolepsy to anger." This insight allows Reynie and his friends to devise strategies to deal with Mr. Curtain effectively, as they can exploit this weakness during their confrontations.

This understanding is integral to the plot and Reynie's development as a character, reflecting his intelligence and keen observational skills. While other options might suggest various vulnerabilities or fears, they do not capture the specific cognitive interruption that occurs in Mr. Curtain when he is enraged, which is essential for the heroes to plan their actions. This demonstrates the importance of recognizing and exploiting the nuances of an opponent's character in a high-stakes situation, a central theme in the narrative.