Terry Pratchett. The fifth elephant (№ 282447)

"That's really stupid, indignant, cynical, but much reduced part of his "I". - It is fake, Lipa, something made in Ankh-Morpork to order and have cost the lives of several people. This Cake is not real! She can't be real!"
But when he heard the universal sigh, Vimes realized, and yet it's real - for all those who need to believe and whose faith was so strong that did the truth is different from fact. For all of the dwarves gathered here yesterday, today, and tomorrow the Cake was the thing itself and the thing in itself.