Why must a full UTXO be spent when sending KAS?

In Kaspa, a UTXO (unspent transaction output) must be consumed in its entirety — you cannot send only a slice of it. Think of a UTXO like a physical banknote: if you hold a 500 KAS note and want to pay someone 100 KAS, you hand over the whole note. Kaspa routes 100 KAS to the recipient and automatically sends the remaining 400 KAS back to you as change. Your wallet software handles all of this behind the scenes, so no manual step is required on your part. Understanding this prevents confusion when you see an unexpected outgoing amount in your wallet history — the extra movement is simply your own change returning to you.