The audience deserves better than a half-baked presentation. If you give them less than your best, they would know. They would feel it in their sinews if you are bluffing through your performance, pretending you know what you are doing.
You may have heard it said before: you must know your act so well you can do it in your sleep.
That’s a good hyperbole. And an excellent advice.
You ought to remember it—while you are awake.