One of the biggest challenges with written language is communicating our ideas effectively to a reader who is not present. When the message is accurately transmitted, written language is amazing. But when the message is inaccurately transmitted, fury encourages us to blame the other person, writer or reader, for the mistake.
The challenge of transmitting accurate messages is that we each use language differently, have different language experience, and function at different levels of expertise within our language. Ultimately, this is why knowing your audience or at least considering who they might potentially be, is so critical to our messages' success.
When we write, we have to think about who we are writing to and what we know about their needs and language skills. Frequently, we don't actually know anything about the person, in which case we have to go with the lowest common denominator.
To communicate with a broad audience, our sentences must be short. Our vocabulary must be simple. Our messages must strive for directness more than linguistic agility. The more we think about our audience and revise our language to meet that audience's needs, the more clear our messages will be.