xkcd #3232: Countdown Standard
Title text:
Anyone who is caught counting 'three ... two ... one ... zero ... GO!' will be punished with a lifetime of eating only ISO standard food samples.
Transcript:
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Source: https://xkcd.com/3232/
Apollo 11 voice goes '4, 3, 2, 1, 0, liftoff'.
Liftoff is a non-integral byproduct of the countdown, not an actual canon part of the sequence.
If you don't say liftoff then the rockets don't ignite.
You ignite the rocket before liftoff though?
Right, but if you don't say it, they won't have ignited.
It's similar to the reason rain dances work. They don't stop dancing until it rains.