Mages know that all humans shape the world with their wills, but Sleepers do so unconsciously - reality is what the majority of people believe it to be. For any individual willworker to work magic, he must force his belief on the world, fighting the billions of minds whose beliefs shape the Consensus. Subtle or coincidental magic seeks to act in tune with the paradigm established by the Consensus, and is thus easier than obviously unnatural vulgar magic. When a mage contradicts the Consensus, it fights back in the form of Paradox.
Magic was more easily practiced before the Age of Reason, a time known as the "Mythic Age" when the majority of humans truly believed in superstition and folklore. In those days dragons, monsters and other magical creatures walked the Earth, it was simpler to travel to the realms of faerie and spirit, and mages could enact powerful spells in front of mortal witnesses with relative ease.
In the modern age, however, the Technocracy has succeeded in manipulating the beliefs of Sleepers to create a much more static and ordered Consensus based on science and reason. The original Order of Reason sought this outcome for altruistic reasons, fearing the power the supernatural held over common folk, but the modern Technocracy seem to enjoy the power this brings them. It should be noted that their great success has made it difficult even for themselves: while it is more in tune with the Consensual paradigm to create an android than a golem, for example, such hyper-advanced technology may still be rejected by the ever-more static Consensus. In the Final Nights, even technocratic mages find their magic is not always reliable or free from Paradox.