Even if it's not connected to the internet but runs on a completely and perfectly airgapped network, when your sensitive data fit on a single USB stick, it's ex

Even if it's not connected to the internet but runs on a completely and perfectly airgapped network, when your sensitive data fit on a single USB stick, it's extremely hard to protect them, simply because of logistics. In the pre-digital age you could maybe steal individual records, but stealing large mountains of papers would have alerted the security guards. Nowadays you can carry truckloads of data in your pocket.