Unbootable systems in the dozens. I think I’ve only fucked up the kernel itself a few times. But grub or other bootloader tons, desktop environment tons, and getting into states so broken the only readily available option was reinstall, dozens. Thankfully most of these were right after a fresh install. For example dual booting just doesn’t work right for some OS installers and grub fails. Manjaro bricked itself after an update. Etc. etc.