This document discusses lessons learned from building projects using lean UX and design thinking principles. It outlines the typical project process including design, build, challenges and solutions. Key lessons include numbering design thinking cards, conducting empathy interviews, prototyping for empathy, focusing research on validating hypotheses with users, and triaging stories for the best cross-functional pairs. The document promotes integrating product, design and development into one team to follow an iterative process of thinking, making and checking.