Double-entry emerged among Venetian merchants in the 1300s and outlived every accounting technology since. What property explains its survival?

B. Redundancy that self-checks: most errors break the constraint

The duplicate entry is deliberate redundancy, and redundancy is what turns a ledger into an error-detecting code, the same principle as a checksum. It costs twice the writing and catches most mistakes automatically, which is why Pacioli's description of it in 1494 still describes modern systems.