Predetermined forces will play the role of fates in the final scenarios. They are unchangeable destinies. In short, they must be predictable within the time frame of the scenario. What they will think and want may be unpredictable and uncertain. We might guess, and we even might strongly feel, that some outcomes are probable, but we can't be sure.
Most forces are similarly uncertain.
We can't predict them, but, as we design scenarios from these uncertainties and predetermined forces, we can become far more aware of why events might move in one direction or another. Sometimes many bouts of between-session research are needed. A Green-based religious movement or global climate cooling or the opening of borders to the free movement of labor might all be considered wildcards. They hover about, tantalizing the scenario plots. Composing the Stories At this point, typically, we have papered the room walls with scribbled notes about potential eventualities, and a wave of anxiety and gloom overtakes us.