Dune is literally about how the future is not what we make it, but that we can and often become subjects to material and historical forces that are larger than ourselves, with events set in motion far beyond even our own birth, set by actors over whom we have no control.

Case in point, Paul becomes emperor, doing the only thing he could possibly have done in order to survive the revolution he started, but in order to do so he not only lost the trust of the only person he ever loved romantically (and who literally taught him to be the person who would become emperor) but also set the empire on the course of a genocidal jihad, all to simply preserve himself and house Atriedes, a path that, in the books, he constantly questions was the correct thing to do, even lamenting upon it, but never having the courage (or even ability) to stop the events that he himself set in motion.