Recently I read, "Marketing begins and ends with your clients." I understand the message - without clients you have no business - but I disagree with the statement. When planning to market, you need to start with "You" - who you are, your knowledge, skills, expertise, strengths, personality, what you can offer, what you care about!
Now it's time to continue to map your Marketing Circle by defining your "Client."
Tell means "to relate in detail; to give utterance to," while teach means "to cause to know something; to cause to know how." Telling requires nothing on the part of the audience. In fact, it doesn't require an audience at all. You can tell a recorder or you can tell thin air. Teaching, by contrast, requires learning. Thus, teaching requires both a teacher and a learner.