The decision by Facebook to adopt Mercurial over Git for their version control was driven by performance considerations and the collaborative nature of the Mercurial community, as detailed in a narrative recounting the company's migration process in the early 2010s. Initially, Facebook faced performance issues with Git due to the scale of their codebase, which led them to explore alternatives, including Mercurial, which offered a cleaner architecture and extensibility. Despite initial resistance from Git maintainers to improve performance for large repositories, Facebook found Mercurial's community more open to collaboration, which, coupled with the system's ease of extensibility, made it a suitable choice. The transition was managed through careful internal communication and alignment with the engineering team, emphasizing the human and collaborative elements in technical decision-making. This strategic migration not only improved Facebook's handling of large monorepos but also led to the development of novel workflows like "stacked diffs," which later influenced other companies and inspired efforts to integrate similar features into Git.