Previously I speculated that there is a vicious circle in cultures that systematically discount the future (as some do). Some parts of the world are better or worse at waiting for Mischel's marshmallow and delaying gratification. In parts of the world where life is very unpredictable, discounting the future may actually be a more rational strategy. It's plainly not as smart to wait another month for a 5% greater reward in, say, Congo as it is in South Korea. Unfortunately, in the aggregate, this kind of decision-making is likely to feed on itself and slow development.
As it turns out that, Kidd et al show in Cognition that at least on an individual basis, children do indeed more strongly discount the future more when that future is less predictable in the traditional Mischelian paradigm.