I re-read the quote from John Steinbeck. I think I understand his concern.

As artists we have a certain image we'd like to convey. Suppose I have an image in mind of a salted pretzel made from a guitar neck. I have the image clearly in mind, but I have no control over what you might see in your mind's eye if I paint or draw it.

On top of that, I never liked how my paintings or drawings turned out because I couldn't get them to exactly resemble the image in my mind. But folks seemed to like the stuff I did.

In the end, all that matters is how the viewer/reader perceives the result.