I’m a big Seth Godin fan, and usually find his blogs insightful and thought-provoking.  Rarely, I disagree with them entirely.  Recently, Seth posted the following blog, with which I disagree so violently that I have to blog in opposition: 

Rehearsing is for cowards
Jackson Browne gave us that advice. He would rather have you explore.
Exploring helps you figure out what you can do the next time you present or perform or interact. Rehearsing . .  . means figuring out exactly what you're going to do so you can protect against the downside, the unpredictable and the embarrassing.
I'm not dismissing study, learning, experimenting or getting great at what you do. In fact, I'm arguing in favor of this sort of hard work. No, I'm talking about the repetition of doing it before you do it, again and again. Just drilling it in so you can regurgitate later. Better, I think, as they say, "…let's do it live."
A well-rehearsed performance will go without a hitch. An explorer seeks the hitches, because hitches are the fissures and chasms that help us leap forward.

For public speakers, this is terrible advice.  I often work with executives who say, “I don’t want to rehearse.  I’ll just get stale.  I’m better when I wing it.”

And when they wing it, what happens?  They ask the first person they see, after the talk, “How did I do?”  Of course, the first person is the Senior Vice President for Stuff, and he says, “You were great, Chief,” because that’s his job. 

In fact, what happens when you wing it, or you don’t rehearse, is that your body language signals to the audience, “Hey, folks, I’m doing this for the first time!”  It's unconscious, but the audience picks it up subliminally right away.  Now, some people are terrified when they’re doing something for the first time, and some people are merely excited, but everyone is at least a little uncertain. 

If a little uncertainty is what you want to telegraph to the audience, then by all means don’t rehearse.  But if you want to show up, instead, as confident, or cool, or in charge, then you need to rehearse

The idea of getting stale is widely misunderstood.  It’s your job as a speaker to show up for your speech with 3 things:  a great talk, a passion for your subject, and a willingness to listen to your audience.  To have a great talk – which means knowing it thoroughly – you have to rehearse.  If you bring your passion to the performance, you will never look stale or canned, because you will be genuinely there, in the moment.  And similarly, if you show up in the moment, you will be able to listen to your audience. 

That’s why you have to rehearse.  And that’s why Seth’s blog, just this once, is terrible advice for public speakers.