Because you’re unlikely to write a good abstraction until you need it more than twice. And if you only need the code twice, you very likely wasted time writing

Because you’re unlikely to write a good abstraction until you need it more than twice. And if you only need the code twice, you very likely wasted time writing the abstraction because copying updates between the two locations is not hard. This is a rule of thumb, I’m not trying to tell anyone how to do their job.