Which aspect of storytelling does the 'evil twin' trope primarily explore?

The 'evil twin' trope primarily explores the duality of human nature and inner conflicts, as it emphasizes the struggle between good and evil within a character. This motif draws attention to the contrasts that exist within individuals, often portraying two sides of the same personality. The 'evil twin' can represent suppressed desires, moral conflicts, or the darker aspects of one's identity that one might grapple with internally. This duality can prompt readers to reflect on their own inner struggles and the complexity of human behavior, making it a powerful element in storytelling that delves into psychological themes. In contrast, the other options focus on themes like friendship, personal sacrifice, and teamwork, which, while important in various narratives, do not capture the essence of the 'evil twin' trope as effectively as the exploration of internal conflict and duality does.