Former Mexican President Vicente Fox is a big booster of the nascent cannabis industry, but he warns against "excessive optimism." "Everybody thinks they're going to make billions overnight," Fox told Business Insider in an interview. "No, they're not. It's a new industry. You have to build brick-by-brick." Fox sits on the board of Khiron Life Sciences Corp, a Canadian cannabis company with significant operations in Colombia. He was in New York speaking with investors. Former Mexican president Vicente Fox is a big booster of the nascent cannabis industry — but he warns that it's not a "gold rush."