It all depends on how you, and your audience, define "success." Believe me, your audience doesn't expect perfection. I used to think most audiences did, but I was wrong! Before I discovered this, I used to put incredible pressure on myself to deliver a perfect performance. I worked for days to prepare a talk. I stayed up nights worrying about making mistakes. I spent hours and hours rehearsing what I was going to say. And you know what? All this did was make me even more anxious! The more perfect I tried to be, the worse I did! It was all very disheartening (not to mention unnecessary).
The essence of public speaking is this: give your audience something of value. That's all there is to it. If people in your audience walk away with something (anything) of value, they will consider you a success. If they walk away feeling better about themselves, feeling better about some job they have to do, they will consider you a success. If they walk away feeling happy or entertained, they will consider their time with you worthwhile.
Even if you pass out, get tongue-tied, or say something stupid during your talk . . . they won't care! As long as they get something of value, they will be thankful.
They don't even need to feel good to consider you a success. If you criticize people, or if you stir them up to ultimately benefit them, they might still appreciate you, even though you didn't make them feel good at the time.