The right word or combination of words can be like the key that fits the lock and opens the door. Sometimes you just can't find it.
Have you ever spent hours composing an e-mail consisting of just a few sentences? (I have, many times.)
Then of course there is the other problem, at least for me, of being overly attached to a word that is too loaded to work effectively. That can get you locked out by causing a bad reaction in your intended audience.
I guess that's one thing that effective communication comes down to--you have to relate to your audience. You can use the right words and unlock the door, or use the wrong words and lock yourself out. And the thing is, the right word and the wrong word may actually be synonyms.
So I guess the question becomes: how do you know when the word is right?