Commmunication is a layered cake, the first layer is being clear about exactly what it is what you want to say. The second layer is knowing how to say it. The third layer is knowing your audience, and how to communicate to that particular brand of people.

Communication is an extremely hard discipline because it requires you to both be knnowledgeable about whatever it is you have to say, being linguistically proficient, and having a good knowledge of people and psychology.