Re-reading Schelling's Micromotives and Macrobehavior...the last chapter is a version of his Nobel acceptance speech on how a norm of non-use of nuclear weapons has developed over the lastr sixty years.
The norm Schelling refers to can be operationalized: We can call it shame that reduces the payoffs of a player who uses nuclear weapons when the other does not by the amount that the other loses from one's decision to use nuclear weapons. Below are two matrices: The one on the left assumes egoism, while the one on the right assumes shame applies.
USE-NO USE--EGO USE-NO USE--SHAME
Use No Use Use No Use
Use -10, -10 1, -15 -10, -10 -14, -15
No Use -15, 1 0, 0 -15, -14 0, 0
The game with egoistic players is a prisoner's dilemma, with using nuclear weapons as the dominant strategy and the only equilibrium. The game with shame is a stag hunt, with no dominant strategy; in that game both use, use and no-use, no-use as well as a mixed strategy are equilibria.