My impression is that it was a combination of three things: internal Windows team dysfunction, ambition too far ahead of the storage and network technologies of

My impression is that it was a combination of three things: internal Windows team dysfunction, ambition too far ahead of the storage and network technologies of the day, and lack of a clear customer use case at a time when the focus of Windows+Office shifted towards enterprise. The OO database storage project was apparently Bill Gates's personal baby, so it didn't lack in executive support. That probably explains why the dream was kept alive for over a decade (Cairo started in 1991, WinFS was finally left out of Vista in 2006). Steven Sinofsky's interesting online book "Hardcore Software" has some chapters about Cairo and later WinFS: https://hardcoresoftware.learningbyshipping.com/p/020-innovation-versus-shipping-the https://hardcoresoftware.learningbyshipping.com/p/020-innova... "Cairo aimed to advance personal computing with dramatic changes in how we thought of files—rather than single files and folders, Cairo intended for files to have the capabilities of a database. Everything on your PC was to be stored in a database to easily search, find, and show relationships between items: files, email, contacts, photos, documents and more. Advancing storage was a long arc of innovation Bill favored. "Ultimately, the human toll of Cairo was high in the sense that so many people spent so much time early in career working on a project that not only didn’t ship but was viewed as squandering resources, at best, and misguided at worst. It was a bit of a black eye for Microsoft among the press and analysts who believed Microsoft would deliver on the idea of object-oriented the way that NeXT had done but at scale. The magnitude of the project would leave many people with Cairo war stories for years to come. I wish I could say that the lessons learned would prevent another experience like this from happening, but that isn’t the case as we will see."