It is important to break away from the modern notion that an artist should strive for originality and that a creator has a kind of monopoly on his own designs. A medieval artist was expected to work according to a specific formula, and this must have often meant using designs and compositions with a familiar precedent. In fact, the genius of a medieval illuminator is reflected in the skill with which he could execute an established subject.

christopher de hamel, history of illuminated manuscripts, pgs.194-195