Digital objects like files and text are easy to duplicate. However, duplication is not a desirable trait in money. This is the double spend problem: how can a receiver of digital money be sure that the money they were sent was not simultaneously sent to someone else? How can all members of a monetary network be sure others are not duplicating their money at will?
Bitcoin solves the double spend problem by using a distributed ledger, which all users can access. When one user sends bitcoin to another, they destroy the coin they own and create a new coin for the receiver. The destruction of the sender’s coin is recorded for all to see, so that they can never send it to someone else.