2017年に￥1,582,858でBTC-USDを買っていたら...

Bitcoin (BTC) is a decentralized digital currency introduced in a 2008 white paper published under the name Satoshi Nakamoto, with the first block mined in January 2009. It runs on a public blockchain maintained by a distributed network of nodes rather than a central bank or administrator. New coins enter circulation through mining, and the protocol caps total supply at 21 million, with the issuance rate halving roughly every four years. Transactions are verified by proof of work and recorded permanently in a shared ledger. Bitcoin also trades continuously, unlike stock markets, so its price series has no weekends or market holidays - which is why a Bitcoin scenario on this site is measured against roughly 365 observations a year instead of the ~252 trading days a stock has.

The network's first block was mined in January 2009, and the first documented commercial transaction came in 2010. Bitcoin's supply schedule is the backbone of its price history: the block reward halves roughly every four years, in 2012, 2016, 2020 and 2024, and each halving has been followed by a distinct market cycle. Along the way the asset has survived several drawdowns of more than 70 percent, including 2014-2015 and 2018, and the 2022 collapse of major centralised lenders and exchanges. Institutional access widened with CME futures in 2017 and US spot exchange-traded funds approved in January 2024. El Salvador adopted it as legal tender in 2021. Because Bitcoin has never had a stock split or a corporate action, its price series needs no adjustment - the number you see for 2015 is the number that traded.

Bitcoin is the asset people most often say they 'almost' bought. Turning that into a figure is more useful than the feeling, because it shows both sides: the multiple you missed, and the drawdown you would have had to sit through to keep it. The year you pick matters enormously - entering in a post-halving year and entering at a cycle top produce results that are not remotely comparable.