When the purpose gets too broad, it gets confused with the subject. Keep these two separate and you're well on your way to focusing your talk. You may have to speak on "Corporate Leadership in the 21st Century"; if you think of that as the purpose of your talk, any panic is justified. A topic like that is just a broad subject; your purpose is to make a specific point about leadership—maybe even in a specific company—through examples, anecdotes, and various facts. So tackle some key trees, not the whole forest. Your purpose in such a speech could be to inform the audience of the skills necessary to achieve leadership in a corporation. Or it could be to convince people to start preparing now for changing leadership roles in the 21st century. The possibilities in the subject are vast, so you must be very clear and specific about your purpose.
The more focused and specific your talk, the better your chances that some words will resonate. Speak vividly about the leadership of one person, and your audience can glean much about leadership in general. Let people make the leap from the specific to the general, while you continue to be vivid. Broad subjects can be wonderful assignments if you give them a narrow—and therefore memorable—purpose and focus.
Always ask yourself how the purpose of your talk relates to your audience's interests. Knowing your audience is the only way to understand its attitudes and anticipate its objections. A dentist addressing a group of parents would talk about preventing tooth decay in their children, not about the latest equipment installed in his office. Study those in your audience; think of their needs. You must link the beliefs you are trying to impart with their existing concerns. Chapter 9 ("Not Meeting the Real Needs of Your Audience") goes into this crucial analysis in detail.