One of the key concepts in Entrepreneurship is validating a business idea before fully committing resources. Payal Kadakia initially launched ClassPass as a search engine for fitness classes named "Classtivity" in 2011. However, the business model didn't gain traction. After pivoting to a subscription-based model based on feedback and market demand, ClassPass found its product-market fit. This pivot is a classic example of how entrepreneurs must be flexible and responsive to market signals.