This really isn't a proverb on trading, per se, but it's one of my favorite lines about the market and trading in general.
As told by Richard Ney in The Wall Street Jungle:
Clearly the lunatic economics of this larceny (stock market trading) appeal to the criminal. The story is told that after he had been deported to Italy, Lucky Luciano granted an interview in which he described a visit to the floor of the New York Stock Exchange. When the operations of the floor specialists had been explained to him, he said, "A terrible thing happened. I realized I'd joined the wrong mob."
As told by Richard Ney in The Wall Street Jungle:
Clearly the lunatic economics of this larceny (stock market trading) appeal to the criminal. The story is told that after he had been deported to Italy, Lucky Luciano granted an interview in which he described a visit to the floor of the New York Stock Exchange. When the operations of the floor specialists had been explained to him, he said, "A terrible thing happened. I realized I'd joined the wrong mob."

