Why is there a countdown before rocket launch?

The phrase "countdown" comes from the 1927 German fantasy feature film "Moon Girl". In this film, in order to increase the artistic effect and exciting, director Fritz designed the rocket launch shot The launch procedure of "9, 8, 7, ... 3, 2, 1" ignition is established. This program has been unanimously praised by rocket experts, who believe that it accurately, clearly and scientifically highlights the dwindling time for rocket launch, giving people a sense of urgency before rocket launch. Since then, "countdown" has been widely used, and has transcended the scope of use, becoming a highly applicable word with a wide range of applications.