This document summarizes the key differences between working as a product manager at a startup versus a big company. It discusses the pros and cons of each, including greater responsibility but lack of resources at startups, and more stability but also politics and red tape at large companies. The document uses an example activity called the "Marshmallow Challenge" to illustrate how larger teams can perform worse than smaller, more nimble ones, relating this pattern to the different environments of startups and big companies.