alt Hacker NewsThe issue with not having a single source of truth is not the fact that you have to update code in 2-3 places, it’s that you have to know to update code in 2-3 places.
Accidental divergence is the problem, not intentional.
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Yes, this is true. And is a bigger problem on large teams. One mitigation is a comment by the original author at both sites that there may be a coupling in the future.
But, again, the point is that you don't know yet whether you have a single source of truth or not. It's a question of the relative badness of duplication vs premature abstraction in cases where the code may diverge or converge in the future. There is no generic answer. But as a heuristic, based on my personal experience, I have always found premature abstractions to be more painful to work with. Even more so when someone else has authored them.
This assumes the bug exists in both places which might not be true at all even if they both are dependent on the same duplicated code.
If you only spot the bug in path A and not path B, why fix the bug for B?