You just have to have a bunch of outs for those type of situations. Like today I was performing for my friends mom, and I lost my break. I sat there for a second, thinking of what to do, when she (luckily) said "I forgot my card.". So that gave me a good excuse to start over. You really have to have good acting skills to make your audience believe that whatever you did, you did on purpose. And remember this: when you mess up, most spectators don't realize you have messed up, and you can start over, or whatever you wanna do. My biggest problem is losing my break. I don't do it alot, but it's my most frequent mistake. One of the things I have tried to do to fix that mistake is to force the card, no matter what effect it is. This way, if you lose your break, you can spread through the deck and ask your spectator "So, you see you're card in there, I didn't make it come to the top like you think I did, right?" And then i'll make a break where their card is, and pass it to the top.
You just gotta be able to improvise.
Anthony Bass