We built a comprehensive pattern library to harmonize our company's design elements and improve consistency across our Intercom product. The library was created as a single source of truth for designers and engineers, but its development revealed unexpected complexities and challenges. We learned that predicting exactly how colleagues work and their needs is difficult, and the library's usefulness varied among team members. Despite these challenges, the library became an invaluable resource for new colleagues during onboarding and has helped shape our team's mindset towards design system thinking. To build a successful design system, it's essential to formulate a clear strategy, allow for customization and local changes, think outside the box, and maintain the library as a living document that reflects the latest state of your product.