In Traditional Finance, What Mechanism Prevents Double-Spending?

In traditional finance, double-spending is prevented by a centralized authority, typically a bank or a payment processor, that maintains a single, authoritative ledger of all transactions. When a payment is made, the central authority instantly debits the sender's account and credits the recipient's account, ensuring the funds cannot be spent elsewhere.

This centralized control and real-time ledger update eliminates the possibility of the same unit of currency being spent more than once.