This is actually a very important principle that science is learning about large systems like evolution and that futurists are learning about anticipating human society: just because a future scenario is plausible doesn’t mean we can get there from here.

Kelly is underscoring a constraint often missed in both evolutionary thinking and futurism: plausibility is not the same as reachability. Complex systems move through path-dependent sequences shaped by constraints, lock-in, and contingent events; some end-states may be imaginable and internally coherent yet inaccessible from present conditions because the necessary intermediate steps are blocked or extremely unlikely. The remark cautions against “just-so” narratives in evolution and against linear extrapolation in forecasting. It also implies a methodological lesson: good predictions must specify viable pathways—mechanisms, transitions, and enabling conditions—not merely attractive or frightening endpoints.