If a file would ruin you leaked, it does not belong on your phone
Most people keep their most dangerous files in the same place they keep memes.
ID scans in camera roll. Signed contracts in email. Tax PDFs in a downloads folder that iCloud copies to three other devices. A roommate, a stolen phone, or a screenshot is all it takes.
A vault is not about hiding. It is about a single locked place with no public link and no shared folder. You open it. Nobody else does.
If you would be sick to see a file on someone else's screen, it does not belong in the same app you use to send photos of lunch.
