In mathematics the fudge factor is “a quantity introduced into a calculation in order to “fudge” the results: that is, either to make them match better what happens in the real world, or to add an error margin.” Of course, in art everything an artist does is a fudge factor. It’s all fudge. Is a regular fudge factory.
(Hope I’m not making anyone hungry.)
No matter how carefully an artist draws (and artists should always draw carefully), one can never draw the world the way it is. If you drew the world as it is, your drawing would need to be one-to-one. And that sheet of paper is just too big.
So what you leave out and what you put in matters enormously. And half of the genius of art lies in getting stuff wrong. We live in the land of metaphor and analogy.