Bitcoin is created by mining and then flowing through the system using the UTXO structure, so that each bitcoin can be traced back to the block where it was born. Such a perfect design completely ensures that bitcoin cannot be counterfeited.
For example: I sent 0.1 bitcoin to my neighbor, why would he believe it was real? Or, how does he believe I didn't transfer this 0.1 bitcoin to two or three people at the same time? This has to do with bitcoin's UTXO structure.
The so-called "UTXO," which means the unspent transaction output, is a core concept for generating and validating bitcoin transactions. Every transfer in the bitcoin world can be traced back to the last transaction. Every payment can be traced back to the previous collection.
The 0.1 bitcoin I give you must be the bitcoin someone gave me that I haven't spent yet. And then you can go all the way back to the block that the miners dug out when it was born. This mechanism guarantees that bitcoin cannot be forged and cannot be paid repeatedly.
Double payments are easy to understand. It literally means that a sum of money has been paid multiple times. In the bitcoin world, this is called "double payments". Before bitcoin, no digital asset could solve the double-flower problem, but satoshi nakamoto used this mechanism to solve the trust problem, so that bitcoin can be widely used.