This lecture explores the concept of personalized health through the lens of a fly as a model organism, discussing reductionism and holism in biological thought, the integration of biological levels, and the emergence of systems medicine. It delves into the use of Drosophila as a tool for studying symbiosis, the Fly Cell Atlas, and the microbiota in 4Ps Medicine, emphasizing the distributed and interactive nature of biological causality. The lecture also touches on the challenges and possibilities of integrating holistic models and measurements in the context of 4Ps Medicine.