The WIP limit (work-in-progress limit) is the concurrency bound on closure: at most 2-3 plans in the Active column of the board at any time.
This is not arbitrary. Too many simultaneous partial closures means none complete. Energy disperses. The system thrashes without making progress toward any single closure condition.
The WIP limit comes from Kanban practice (Anderson, 2004) and is reinterpreted here as a constraint on how many closure processes the system can sustain concurrently.