A commitment said out loud in front of witnesses closes exits that a private intention leaves standing open.
Declaring whose you are converts a preference into a commitment, because a person cannot live long with a visible gap between a stated identity and ordinary behaviour. The avowal and the walking are one act, not a promise followed by the effort of keeping it.
What follows runs on its own power: the declaration sets the standard, the standard sets what a person will tolerate in themselves, and that intolerance does the work on unremarkable mornings when nobody is inspecting. Kept quiet, the same decision stays negotiable, and anybody can revise what they never said to another soul.