Perhaps the worst fear of any musician is a live performance mistake. Your going along just fine and dandy and all of a sudden you pluck the wrong note, press the wrong key, or hit the wrong drum. It sounded awful. Your band-mates (if you have any) are giving you looks. You feel stupid.
Well you shouldnt. In my talks with people that are part of an audience when I perform, most of the time they say that they didnt notice the mistake. Even if I point out the specific point in time it happened, they dont notice.
But why is this?
Honestly, most audience members are relatively dumb when it comes to the structure of music. They really dont know how it is supposed to sound. The only time they would notice is if it is glaringly obvious. If your voice breaks for example (especially if you are singing solo, I did it once, but, thankfully, I was with a chorus), or if you hit a note so very wrong that no one could help but noticing it.
You have to remember that you and I are musicians. We notice every little detail. If something goes wrong, no matter how trivial, we recognize it right away.
Let me tell you a story. A few weeks ago I got the opportunity to play in front of a large-ish group of people at a church service along with three other people. Two days earlier I had replaced my guitar strings. Over those days I had played my guitar a lot in order to stretch out the strings. It didnt work. My guitar did not stay in tune.
I was distressed. Thankfully we had another guitarist who could pick up the slack. In the meantime, I had to play my guitar very carefully in order to make sure that everything would sound OK. The only people who noticed were my band mates, the sound technician, and a few people who knew me well enough to tell that I was preoccupied.
So you see, you need to worry less about your exact sound when you perform. Even in the case of the more obvious examples, there is a good chance that they will forget it by the end of the performance as long as it is good enough for them to focus on.
Have you ever done something terribly obvious that you felt completely stood out in your performance (in a bad way) if so, what? And did anyone notice?