When it comes to expressing the act of disappointing or failing someone, the phrase "let someone down" may sometimes feel overused. Luckily, the English language offers various synonyms to convey this sentiment with different shades of meaning. One alternative would be "disappoint", a simple yet effective term that encapsulates failing to meet expectations. Another option is "fall short", which implies the inability to reach a desired outcome. "Betray" suggests a breach of trust or loyalty, while "fail" denotes an inability to fulfill one's obligations. Additionally, "underperform" stands as a substitute, emphasizing the failure to achieve at an expected level. These synonyms enable us to articulate the act of letting someone down with nuance and precision.