First, the question of deduplication a/k/a normalization. Deduplication is cheap, and it's "a two-way door, not a one-way turnstile:" It's cheap to re-duplicate when you find that one of the users of your de-duplicated function or whatever needs new behaviour.
Second, there is the question of the right versus wrong abstraction: If two different things use the same thing, that doesn't necessarily mean that they share the same abstraction conceptually. But of course, sometimes the duplication is a hint that there is some semantic commonality, and when you get this right, it's glorious, but if instead of de-duplicating we actually build the wrong abstraction, it can be extremely expensive to fix. That's more of a "one-way turnstile" problem.
To me, when I see code that could be "DRY'd up," I have to ask myself whether it represents an opportunity to write a better abstraction, but I treat that decision conservatively, because of the cost of getting it wrong. In many cases, I choose to de-duplicate the code without creating what might be "the wrong abstraction," and it is often less expensive and lower risk to start there and only later consider abstractioneering.
p.s. The tension between de-duplication and abstractioneering resembles the tension between is-a and has-a, often expressed by classical OO programmers as "inheritance" In those terms, I'm really describing my inclination as "Prefer composition to inheritance by default."
p.p.s. Sandi Metz asserts that de-duplication is creating a new abstraction: https://sandimetz.com/blog/2016/1/20/the-wrong-abstraction. I feel that there is a sliding scale from "extract method" to "These two things share a superclass with a private message," but read her thoughts and come to your own conclusion.
First, the question of deduplication a/k/a normalization. Deduplication is cheap, and it's "a two-way door, not a one-way turnstile:" It's cheap to re-duplicate when you find that one of the users of your de-duplicated function or whatever needs new behaviour.
Second, there is the question of the right versus wrong abstraction: If two different things use the same thing, that doesn't necessarily mean that they share the same abstraction conceptually. But of course, sometimes the duplication is a hint that there is some semantic commonality, and when you get this right, it's glorious, but if instead of de-duplicating we actually build the wrong abstraction, it can be extremely expensive to fix. That's more of a "one-way turnstile" problem.
To me, when I see code that could be "DRY'd up," I have to ask myself whether it represents an opportunity to write a better abstraction, but I treat that decision conservatively, because of the cost of getting it wrong. In many cases, I choose to de-duplicate the code without creating what might be "the wrong abstraction," and it is often less expensive and lower risk to start there and only later consider abstractioneering.
p.s. The tension between de-duplication and abstractioneering resembles the tension between is-a and has-a, often expressed by classical OO programmers as "inheritance" In those terms, I'm really describing my inclination as "Prefer composition to inheritance by default."
p.p.s. Sandi Metz asserts that de-duplication is creating a new abstraction: https://sandimetz.com/blog/2016/1/20/the-wrong-abstraction. I feel that there is a sliding scale from "extract method" to "These two things share a superclass with a private message," but read her thoughts and come to your own conclusion.