Explore the challenges and complexities of library development in this 20-minute conference talk from ACCU 2016. Delve into the often-overlooked aspects of creating useful libraries, as David R MacIver shares his experiences and insights. Learn about the unexpected requirements that arise when people start using your library, and understand why writing libraries can be a more demanding task than it initially appears. While the talk draws primarily from Python-based examples, the lessons and pain points discussed are applicable to library authors across various programming languages. Gain valuable perspective on the realities of library development and briefly glimpse a vision for potential improvements in the future.