Inexperienced entrepreneurs and managers in large corporations often treat surprises as failures of prediction or deviations from plan that must be corrected, absorbed, or—even worse—ignored. Effectuation begins from a fundamentally different premise: Surprises are not noise to be filtered out; they are signals to be leveraged. The Lemonade Principle describes how expert entrepreneurs transform contingencies—good or bad surprises—into resources for building their ventures. This note is ideal for use as part of the "Good-to-Go Effectual Entrepreneurship" program (for more information on this program, see Jim Zuffoletti, “Good-to-Go Effectual Entrepreneurship: Educator’s Guide,” UVA-ENT-0245). The program is designed to help students understand effectual thinking; to apply the causal, adaptive, visionary, and effectual (CAVE) framework to their decisions; and to understand expert entrepreneurs.