30 was a line from the TV series " Just 30 ", which meant that a person should have achieved something by the age of 30. The source of this sentence is a passage in the Analects of Confucius: Political Affairs. The original text is: "I am fifteen years old and I am determined to learn. I am thirty years old and forty years old. I am not confused. I know the destiny of heaven. I am sixty years old. I am seventy years old and I am obedient. I do what I want without exceeding the rules." This passage emphasized that a person should pay attention to learning, thinking, understanding himself and destiny in the process of growing up. By the age of 30, he should establish his own outlook on life and values and be able to cope with various difficulties and challenges. At the same time, this sentence also reminded people to cherish time and constantly learn and grow to achieve their life goals.