Bill Jensen, The Simplicity Survival Handbook, 2003:

Every day, you must communicate to tens or hundreds or thousands of people who are instantly deciding whether they buy into whatever you’re saying, and whether they should act. Most will give you only seconds to grab their attention and convince them. Lack of clarity and focus has been called the Silent Career Killer. Few in your audience will tell you that you were unclear. But they’ll remember! We must all compete on clarity. Every day.