All the confidence that this person used to have has gone out the window, replaced by anxiety and self-doubt.
After talking to this client and listening to him run through the outline of his presentation, the first thing I told him was that he came across as warm, friendly, approachable and likable, and that this was going to be a huge factor in his success.
The surprise in his voice actually made me a bit sad. He told me that no one had ever told him that, even in his previous speaking training. It made him feel so much better to know that JUST BEING HIM was going to be a benefit to his speaking. That JUST BEING HIM was a good enough place to start.
I find that speakers worry so much about the techniques, the words, their physical appearance, the "ums," the quiver in their voice and the potential for mistakes, that they overlook the major factor of embracing who they are as a person and just connecting with the audience from that place.
I'm not saying that speaking skills aren't important - if that were true, I wouldn't have a job. You still have to learn how to develop and structure an effective presentation and deliver it successfully in a way your audience can understand and remember.
But no amount of skills and polish can overcome your own negative (or even shaky) perception of yourself.
If you feel that you're not good enough ("... smart enough. And doggone it, people like me." I couldn't resist...) as you are, as a person, that insecurity is going to ooze out all over your presentation. In your posture, in your voice, in your facial expressions, in your movements.
You may not be an expert on your topic; your boss may be pushing you to speak on something you know little about. It happens all the time. For that matter, you may work for yourself and be new to your topic and still learning.
The point is: That's okay. You'll get it eventually. You'll keep learning (as we all do) and one day you'll have no qualms whatsoever about standing up and addressing that topic.
But right now, be confident that you are good enough as you are. Make a human connection with the audience like you would with a good friend or beloved family member. Fall in love with the real you and the rest will fall into place.