"The only ___ is mediocrity": Martha Graham

SIN

["Consider what Martha Graham might have viewed as a moral failing in art."]

This clue quotes Martha Graham, a famous dancer and choreographer, who said, "The only sin is mediocrity." The answer is "SIN" because it directly fills in the blank from her statement. The wordplay is straightforward—no tricks—just a direct reference to her well-known phrase about striving for excellence.