On January 8, 2018, the cryptocurrency market experienced a sudden and sharp decline in value that began not with a mass sell-off, but with a change in how prices were calculated. CoinMarketCap, which was the most widely used price-tracking website at the time, decided to remove South Korean exchanges from its global average calculations without prior warning.

This change was made because digital assets in South Korea were trading at significantly higher prices than the rest of the world, a phenomenon known as the Kimchi Premium. At the time, high demand in Korea combined with strict government rules on moving money out of the country meant that Bitcoin and other coins often cost 30% to 50% more there than in the United States or Europe.

When CoinMarketCap excluded these high Korean prices from its data, the displayed prices for almost every major cryptocurrency dropped instantly on the website’s dashboard. Ripple (XRP) was affected most visibly, appearing to lose over $20 billion in market value in a single moment as its price on the site shifted from $3.19 down to $2.67.

Because many investors and automated trading bots relied on CoinMarketCap as their primary source of truth, the sudden appearance of "red" numbers across the board caused immediate confusion. Without an explanation on the website's homepage, many traders assumed a real market crash was happening and began selling their holdings. This turned an atmospheric change in data into a physical sell-off.

By the time the website issued a statement on social media hours later, the momentum of the decline had already taken hold. This event occurred during a period of high tension, as the market had just reached record highs in late 2017. A few days later, the South Korean government announced potential plans to ban crypto trading, further driving prices down. The events of early January served as the starting point for a prolonged market downturn that lasted throughout the rest of the year.