What Should Trigger a Change of Plan?

Scenario planning is useful only if a scenario can change a real decision—not just produce another document on the shelf.

Suppose a team agrees on a backup plan, but the signals are ambiguous. What evidence should trigger a shift from the current course to the contingency? Who should own that call, and whose input is essential before acting? I’m especially interested in how teams set a threshold that is clear enough to use without pretending uncertainty has disappeared.