One of the biggest challenges for digital currencies is preventing Double Spending. This is when a user is able to spend the same amount of Bitcoin twice. If a digital currency allows double spending to happen then trust in the system is likely to be compromised.
Bitcoin manages to solve this issue thanks to confirmations and its proof of work consensus mechanism. This means that every transaction sent from an address must be “confirmed” by multiple validators before it can be processed. Multiple mining computers look at data on the blockchain to confirm users have the balance they claim and compare their findings. Only after confirmations from multiple miners have been made is the transaction sent, therefore preventing double spending from taking place.