system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we count down from 3? And why do our brains like the ‘rule of thirds’?
gpt
I believe it’s cause we need three numbers to establish a pattern. 

1...0 isn’t clear when the zero will come

2...1...0 is still tough to predict because we don’t know for sure that the gap between 2 and 1 will be the same as 1 and 0

3...2...1...0 is helpful. If the time between 3 and 2 is the same as the time between 2 and 1, then we have a pattern and can infer the amount of time between 1 and 0.  Using three numbers allows us to know when 0 is and thus when the event or action will occur.