The document discusses sizing markets for new technologies and products. It notes that accurately predicting market size is difficult as markets can evolve rapidly. It recommends starting by talking to potential customers to understand market needs without revealing your unique business idea. Additionally, it suggests analyzing competitors, historical trends, and using a "lean" approach to test the market and gather feedback. Overall, the document emphasizes getting a realistic view of the market through research while acknowledging forecasts will likely be incorrect. The market ultimately decides how big it will become.