I think most of us have a larger "understanding" vocabulary than our "user" vocabulary. By that I mean I rarely have to refer to a dictionary, as I read, to understand a word's meaning, but I do need a dictionary and thesaurus as I write. I tend to write in a simplistic manner, using the same old words over and over, when an alternative word would add a dash of pizazz.
Take the word "sat". for instance. Quinn sat in his favorite chair. Now notice the visual that comes to your mind when I replace sat with another. Quinn eased into his favorite chair. Or...Quinn slumped in his favorite chair. How about...Quinn sprawled in his favorite chair. Notice the visual that comes from changing one word in a sentence?
Which sounds better? Quinn hit George repeatedly...or...Quinn pummeled George repeatedly. Quinn walked into the room...or Quinn scurried into the room. One could replace walked with tripped, sauntered, stalked or trudged. Each word gives a different visual. Since we want our readers to mentally visualize what we're putting down in black and white, we need to chose the right word. For me, that can be a challenge.