Last week, I had two different students approach me with the same particular frustration: they have this great idea and they see it so clearly in their heads - but they just can't seem to transport it to the paper in a way that the reader can "see" exactly what they want him/her to see.
We talked about how that's probably the greatest challenge of writing - transporting the picture you see in your own head to the page - and then from the page to the reader's mind. Sometimes, that picture can get lost in translation. Sure, I would love it if readers "saw" my characters, my plot, my ideas, exactly the way that I see them in my own head, detail for detail. But the truth is, that's virtually impossible.
For instance, if I tell you to picture a tree with three branches, thick with emerald-green leaves, the image in your head might come close to mine, but it won't be identical. My tree will look different than your tree. It might be shorter, or the branches might lean in a different direction from yours. But I suppose that's the beauty of it all - because we're different people with different perspectives on the world, our interpretations will be utterly unique.
So, my suggestion to my students was to relax, and do the best they could do with the tools in their writing toolboxes - dialogue, imagery, characterization, setting - in order to place their unique vision onto the page. Then, to let it go. At that point, even if the reader's vision ends up being slightly different, it's okay. Because in the end, a tree will still be a tree.