Seoul: The benchmark Kospi crossing 8,000 points marked a new milestone for investors in South Korea. Yet it also exposed how quickly celebration can give way to unease. On Tuesday, the index closed at 8,047.51, up 2.55 percent. It rose again on Wednesday to 8,228.70. By Thursday afternoon, however, it had fallen nearly 4 percent before recovering to close at 8,185.29. In three sessions, the market delivered both a milestone and a warning.

According to Yonhap News Agency, the latest rally has been driven by a global surge in demand for artificial intelligence chips, propelling Korea's semiconductor leaders and drawing in capital. The Kospi doubled from 4,000 in late October to above 8,000 in just over six months. Such rapid growth invites admiration, but it also embeds expectations that can prove fragile. What sets this cycle apart is the concentration of market gains. Samsung Electronics and SK hynix now account for roughly half of the index's market capitalization. Even at the latest peak, only 75 stocks rose, while 826 fell, suggesting a market increasingly driven by a narrow set of winners, with capital drained from the broader field.

Into this environment, a new accelerant arrived midweek as 18 single-stock leveraged and inverse exchange-traded funds tied to the two giant chipmakers began trading. Turnover exceeded 10 trillion won ($6.6 billion) on the first day, constituting about 23 percent of the ETF market. More than 130,000 retail investors rushed to complete mandatory training, briefly overwhelming the system. This was less portfolio diversification than speculative positioning, with average turnover ratios exceeding 200 percent.

The structure of the leveraged products explains both their appeal and their risk. Designed to deliver twice the daily movement of the related shares, they amplify gains in a rising market, as well as losses when prices fall. Given Korea's daily price limit of plus or minus 30 percent, a twice-leveraged product can swing by as much as 60 percent in a single session. After sharp gains at launch, several of these products quickly reversed as the stocks they were linked to retreated, falling by roughly 3 to 5 percent intraday.

The danger extends beyond daily volatility. Leveraged products are path-dependent. In choppy markets, repeated gains and losses can erode capital even if the stocks they are tied to end near where it began. This negative compounding effect makes them ill-suited to long-term investing, despite their popularity among retail traders seeking amplified returns. The broader backdrop heightens the risk, with margin lending balances around a record 36 trillion won. Forced liquidations have surged, with daily sell-offs reaching as high as 145.8 billion won this month. When leverage meets volatility, declines can trigger cascades of selling that deepen losses and unsettle prices further.

Policy has struggled to keep pace. Authorities approved single-stock leveraged products earlier this year in part to draw retail funds back from overseas markets. Yet warnings about the possibility of steep losses were issued only days before their launch. Encouraging risk-taking and then cautioning against it is not a coherent approach. The effects are already spilling beyond equities, with heightened volatility encouraging profit-taking and shifts into real estate and foreign assets. A market that functions as a short-term cash generator cannot easily support long-term capital formation.

None of this diminishes the significance of the Kospi's meteoric rise. Strong earnings and global demand have lifted Korea's market at a remarkable pace. But a durable advance requires breadth and stability. A market dominated by two stocks and amplified by leveraged bets offers neither. The test of a Kospi at 8,000 is not whether it can climb higher, but whether it can do so without magnifying risk. When the summit comes into view, the drop below tends to deepen.