Saying You're Sorry
Of course, you should always be considerate of your audience, and apologizing when you make a mistake may seem like a good thing to do. But that's not necessarily the case. Apologizing when it isn't called for is not only unnecessary, it can actually hurt your presentation.
Unfortunately, many of us were trained as children to apologize as a gesture of politeness. In some cases, we've done it so often, it's become a habit.
If that's the case, it's important that you break that habit. Don’t apologize every time you make a mistake. (“I’m sorry, I lost my place....” or “I’m not as prepared as I meant to be....”) Apologizing points out an error that your audience may not have noticed, and so it draws attention away from your message and toward your mistake.
Apologizing also reduces your credibility as ‘being in charge.’ When you're speaking, your audience expects you to be the authority. Although saying "I'm sorry" once can make you appear human (after all, to err is human) which can help you establish a rapport with your audience, if you apologize repeatedly or unnecessarily, you can appear that you don't know what you're doing or you're unprepared.
Of course, sometimes an apology is appropriate, especially when your mistake is glaringly obvious. In that case, apologize and move on. And remember that if you really need to say “I’m sorry,” don't just be polite — make it sincere.