It comes about as rational actors make informed choices between realistic alternative lifepaths, always taking responsibility for the consequences that those choices will have on their own cumulative life stories […]

Note the two-horse whippletree on the beam at the lower left. (A whippletree, of which this is the simplest possible, balances the load on the animals.)

For example, caregiver reactions may be quite different for a highly irritable, highly soothable child, as compared to an equally highly irritable child who is not soothable.

So a law of nature which said, say, that Ravenhood is causally linked with blackness would entail both All ravens are black and All non-black things are non-ravens, but would not entail a law linking non-blackness with non-ravenhood.