Technically there is no such thing as a bitcoin. Just unspent transaction outputs. Those get spent as an input of a transaction and then are gone forever. There is no concept of the output of a transaction being the same "bitcoin" as what comes from the input of the transaction. This means if you had 2 inputs and 2 outputs of the same amount there is no way to trace which input became which output. At best you can find which outputs potentially came from an input.

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lazide 2 days ago | parent [-]

That is called tracing. It’s also not hard - every node does it to verify blocks.

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charcircuit 2 days ago | parent [-]

When blocks are verified it just needs to validate that sum of the outputs isn't more than the sum of the inputs. It doesn't care about tracking what went where.

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lazide 2 days ago | parent [-]

Except I can literally pull up a full node and see a wallets current balance - which is because it traces all the transactions through the blockchain, verifying all of them.

Literally the only way anyone can see their wallet balance is by doing this.

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charcircuit 2 days ago | parent [-]

You can find your balance by looking at the UTXO set and seeing if your adress can spend it. There is no need to trace where those UTXO came from.

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lazide 2 days ago | parent [-]

But every full node does, because it is required to validate the chain.

Near as I can tell, you just don’t know how Bitcoin actually works?

	▲	charcircuit 2 days ago \| parent [-]
		I will say it again. When validating the chain all it cares about is that the sum of the output UTXO for a transaction are <= the sum of the input UTXO. All the input UTXO are no longer valid once spent and can be forgotten.