Lu Xun's A Trivial Matter was a short story published in 1926. It was a story about a young man who doubted his character because of a small matter, which affected his life path. This article profoundly revealed the complexity of human nature and the importance of self-awareness by describing the protagonist's psychological state. In the first person, the protagonist described a series of events, including his association with a woman, a misunderstanding, and a chance encounter. Through the description of these things, the author shows the contradiction and uneasiness in the protagonist's heart. He feels that he has been deceived, misunderstood, and even began to doubt his own personality and values. Through the description of the protagonist, the author reveals the complexity of human nature and the importance of self-awareness. In this article, the protagonist's self-awareness was destroyed by a small matter, which caused him to reflect on his own behavior and values, leading to a series of psychological changes and behavior changes. Therefore, this article deeply explored the complexity of self-awareness and human nature, which had positive social significance in inspiring people to reflect on their own behavior and thinking.