Of course, the rule of 3 is saying that you often _can't tell_ what the shared concept between different instances is until you have at least 3 examples.

It's not about copying identical code twice, it's about refactoring similar code into a shared function once you have enough examples to be able to see what the shared core is.

But don’t let the rule of 3 be an excuse for you to not critically assess the abstract concepts that your program is operating upon and within.

I too often see junior engineers (and senior data scientists…) write code procedurally, with giant functions and many, many if statements, presumably because in their brain they’re thinking about “1st I do this if this, 2nd I do that if that, etc”.

3 just seems arbitrary in practice though. In my job we share code when it makes sense and don’t when it doesn’t, and that serves us just fine