It's not just what you say. . .

The end of that sentence completes a lesson I think we all learned when we were younger. It's not just what you say, it's how you say it. This is primarily a reference to tone and body language, but what about word choice?

That is what it comes down to when writing. Sometimes, if word choice is poor, the idea a writer is trying to put across can be lost. Enthusiasm must come across on the page. Terror must come across on the page. Whatever emotion you are trying to evoke, it needs to come across on the page.

Literary Agents and Publishers expect no less, as with your readers.