How Many Times a Pattern Repeats Before It Joins the System
Three different product teams have each independently built their own version of a "confirm this destructive action" dialog.
Per this subject's contribution-model heuristic, what does this specific count signal?
The correct answer is "It's the third occurrence — the signal to graduate it into a governed component."
This subject names the practical heuristic directly: the "rule of three." If a pattern gets built ad hoc three separate times by three different teams or contexts, that's the signal it's a real, recurring need rather than a one-off — it graduates from a local implementation into a proposed, reviewed, system-level component. Before the third occurrence, formalizing it is premature; after it, formalizing prevents a fourth and fifth divergent copy from appearing.
The distractors misstate the threshold: five isn't the cited number — three is the specific, named heuristic; formalizing after just one team's build would bloat the library with speculative variants nobody else has actually needed yet; and the heuristic isn't "never promote ad hoc patterns" — the entire point of naming a rule of three is that recurring patterns should be promoted, once the recurrence is real rather than assumed.
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