Explore the fascinating world of Behavioral Finance in this Yale University lecture. Delve into the revolutionary field that applies insights from social sciences to finance, challenging traditional economic theories. Discover how psychological patterns like overconfidence impact financial decision-making and learn about Kahneman and Tversky's Prospect Theory, which addresses irrational deviations from classical models. Examine market volatility through a present value analysis, understand the ubiquity of overconfidence in financial markets, and investigate how people make choices according to Prospect Theory. Finally, explore the Regret Theory and how fashion can be used as a measure of market behavior. This comprehensive lecture provides a solid foundation in Behavioral Finance, offering valuable insights for anyone interested in the intersection of psychology and economics in financial decision-making.