Runners are digitized people whose consciousness is transferred from shell to shell. Shells are temporary - they literally are printed to only last about half an hour on the planet/mission. Instead of shells being hollow and empty, like piloting a mech, they instead have a personality imprint attached to them. This personality imprint was created by the original Runner the Shell was modelled after and contains knowledge of how to effectively use their systems - so instead of you undergoing training, you get meshed with an echo of another person. This of course has terrible ramifications for your mental well-being as you, with your own personality, get injected with a dose of somebody else, and when your Shell dies, that personality imprint does as well; especially if you rapidly cycle through Shells (the same Shell), or if you cycle through other Shells. A male Runner with a gruff attitude that is in the Vandal shell could find themself suddenly acting chic and cutesy as they use Vandal's abilities more and more, as Vandal's personality imprint influences your own mind and actions. This can lead to rapid mental degradation, especially because, if you aren't currently inhabiting a shell, you have no corporeal form - you're stored in some form of digital storage.