Part of the answer to your question is that fictional objects don't exist: in that sense you don't create them. What you create is a kind of specification, like 'a person who knows all the laws of physics'. The specification is real, but there is no real person who fits it. But this isn't the whole answer, because even though we can't create something just by specifying it (or else we would all be rich), it can still seem mysterious that we can even specify a person who knows something we don't know. How can we even come up with the specification in this case? But that is a cool thing about specification: there is a sense in which you can specify a fact you don't know. I don't know the score of the last Red Sox game, but I have no trouble specifying that score: I do it simply by means of the expression (or thought) 'the score of the last Red Sox game'.