The reasoning
Redundancy you can place.
Every offline system has the same weakness: the thing can be destroyed. Fire, flood, a house move, a well-meaning tidy-up. Encryption does not help with any of that, copies do.
Three copies let you spread that risk across places that fail independently: one with you, one at home, one somewhere else entirely. No single event takes all three.
It also lets one card be expendable. The copy that travels can be lost without drama, because two remain where you left them.
Placement
A pattern that works.
-
I
On you
In the wallet, among ordinary cards. The one you would actually use, and the one most likely to go missing.
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II
At home
A drawer, a document folder, a safe. Not the same bag as the first, and not next to your written password.
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III
Elsewhere
A parent's house, an office, a bank box, a lawyer. Far enough that a local disaster cannot reach it.
Three places
that fail apart.All three cards hold the same vault, written by you. Rewriting means updating each copy, which is why the set is three and not thirty.