Final answer:
Brian is startled by his reflection in the water as it represents a version of himself that he doesn't recognize, symbolizing his internal changes and the impact of his experiences.
Step-by-step explanation:
When Brian sees his reflection in the water, it frightens him because he does not immediately recognize himself. The reflection serves as a metaphor for Brian's changed self-perception after undergoing significant experiences. His reflection likely startles him because it shows a version of himself that is different from what he remembered or expected to see, highlighting themes of self-discovery and the impact of trauma. This concept is often explored in literature, where characters confront their reflections to symbolize internal conflict or transformation.