If you want to pass yourself off as a real magician/psychic/whatever you do conjuring tricks [...] if you are in doubt about your ability to repeat the trick you quit while you are ahead.

I know you are talking metaphorically, but an interesting aside:

Professional-level performers pretty much only perform tricks that they are 99.99% certain of. Performers act as if what they are doing is difficult, when in reality, a professional-level performer could do the entire act in their sleep. This is especially true of magicians, where a mis-step will ruin the illusion. Another example is that jugglers will drop on purpose, to show how hard their act is, and to get the audience on their side.