fiat by Laws

See Page XX – an RPG column by Robin D Laws
Loosely determined systems permit the GM to weave a sense of order into the proceedings. Outcomes become reassuringly apt, as in a satisfying narrative, and less like the apparently random, undirected nature of real experience.
This leads to two questions, one philosophical, the other practical.

And this is a good, better, best summary of the debate about diceless and system.