For over a century, a succession of visionaries described what a personal knowledge system should be. None of them built a daily personal instrument that accumulated across decades. This paper describes what happens when a practitioner does. ThetaOS is a personal knowledge system built and used daily since autumn 2025, drawing on structured personal data reaching back to 1972. It consists of 339 relational database tables, over 91,000 records, and 2.577 million words of structured content, with an AI advisory layer that proactively suggests relational links for human confirmation. Building and operating this system under sustained daily practice surfaced four design principles not previously described in the PKM literature: (0) everything exists only once — entity identity as the precondition for relational intelligence; (1) intelligence resides in the data structure, not the AI model; (2) confirmation-driven edge creation as a third path between manual and automatic linking; and (3) a network that grows smarter without growing larger. This is a single-case practitioner report, offered not as empirical validation but as a first account of what becomes visible only from inside the practice. The full paper includes formal methodology, system description, historical context from Otlet to Bush to Bell, and implications for extended mind theory and PKM design.