How can Kaspa scripts attach state to UTXOs?

Kaspa scripts can implicitly attach data — called state — to a UTXO and enforce that the data changes correctly every time that coin is spent. Normally a UTXO is just a locked coin with no memory: it carries a value and a script, nothing more. Kaspa's introspection opcodes combined with OP_CAT and OP_SUBSTR change this: they let the script read details of the current transaction and compare them to the previous one, so the script itself can verify that a stored value (like a counter) was updated according to a specific rule before the spend is accepted. The practical takeaway for a beginner is that this makes self-enforcing on-chain logic possible — a coin that remembers its own history and refuses to move unless the rules are followed — without a separate smart-contract virtual machine.