The software engineering rule of 3

https://erikbern.com/amp/2017/08/29/the-software-engineering-rule-of-3.html

Excerpts:

 first rule of 3. Don’t worry so much about code duplication if you only have two classes or two functions or whatever. When you see a pattern in three different places, it’s worth thinking about how to factor it out.

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 second rule of 3 — you’re not going to get the system design right until the third time you build it.