The sinking sensation of realizing that my entire operating system is spyware that phones home tens or hundreds of times each time I sit down to use it. Massive bloat and poor optimization neutering my otherwise just fine hardware. My operating system deciding it will no longer support my beater legacy hardware.
Really the shift happened when I became privacy conscious, and once I saw that all of my gaming and day to day tasks worked just fine on Linux I decided to go all in.