Thurston's three rules in magic

1. Never reveal the secret to a trick—it ruins the mystery.
2. Practice to Perfection – never show a trick until you can do it properly every time—A poorly done trick inadvertently breaks rule No. 1.
3. Do not repeat tricks in front of the same audience—no matter how much they beg! Most magic is based on the spectator not knowing what to expect. The second time around they will know what to look for, and might spot the secret!