One of the most fun parts about Bitcoin for me is that there are actually infinite public ledgers available. You and your counterparty have to agree in advance

One of the most fun parts about Bitcoin for me is that there are actually infinite public ledgers available. You and your counterparty have to agree in advance on which one you're using. Bitcoiners have solved this coordination problem by saying "We mutually agree to use the public ledger which a) adheres to all the rules in the Satoshi client and b) is longest of all ledgers satisfying that constraint." From this follows several consequences, like there being an infinite supply of cryptocurrencies which share every advantage of Bitcoin, the Satoshi client being really freaking important relative to the "protocol" (whose only authoritative description is the Satoshi client, since in the case of disagreement with the Satoshi client the network will reject you no matter how "correct" your decisions are), and the fact that the ledger which is anointed as consensus at T1 is not necessarily the same ledger which will be consensus at some future T2 when looking back at history.