system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is so much emphasis placed on the first 100 days of the U.S. Presidency...why not 60 or 120 or any other number?

I know that the beginning of a new administration is a good litmus test for how effective it will be, but why exactly 100 days? Is there something specific about what can happen during this timeframe, or is it mostly arbitrary?
gpt
It dates back to FDR's first 100 days in office. During his first 100, he created a madhouse of policy change, bill drafting, signing, and law shifts in the nation. It was considered so intense that it became common place to measure the first 100 days of newer presidents against it. While we no longer compare to FDR for the 100 day rule, it's generally believed that the first 100 can give us insight into what might be the new norm. If they can hold their promises, unify, or in some sad cases. Divide.