Customer development is a process that helps startups avoid building products that nobody wants to pay for. It involves talking to potential customers to deeply understand their needs and problems. This helps companies learn if they are building the wrong thing or how to find customers before launch. There are different stages of customer development - discovery to learn about customers, validation to prove customers will buy, and efficiency to scale sales. The key is to avoid sales pitches and instead have casual conversations to learn from potential customers as experts. Following the customer development process can help startups create successful products that solve real problems.