Intro
WSJ reporter Jack Pitcher explains how South Korea's Kospi went from the world's best-performing stock index to a market its own investors call the Rollerkospi, what leverage did to the individual traders known as ants, and why owning the Korean country index is closer to owning two memory-chip makers than to owning a diversified market. In the first half, WSJ personal technology columnist Nicole Nguyen walks through how to buy a refurbished phone safely as the memory chip crisis pushes new handset prices up.
Guest: Jack Pitcher, Wall Street Journal reporter
Also on: Nicole Nguyen, Wall Street Journal personal technology columnist
Host: Imani Moise
Published: 28 August 2026 on WSJ Tech News Briefing · Kospi interview recorded 27 August 2026
Show notes | 11 min
Key Takeaways
Korea's individual investors act as a bloc, and they used borrowed money to do it
Pitcher on the term ants: "It means they're weak individually, but capable of collective power, just like an ant colony."
What was niche in the US went mainstream in South Korea
The Kospi's summer drop compressed a financial-crisis-scale decline into weeks
"That's a huge drop equivalent with what the entire US market did over several years during the financial crisis just happening in a few weeks."
The country index is not the diversification buyers think they are getting
The show's own figure: the two chip giants "accounted for more than 50% of the Kospi's value" by mid-2026
A laid-off sound engineer put his entire severance into the Korean index
"he lost almost half of it just within a week"
The unwind starts as psychology, not as news
A stock that has risen day after day drops 5%, holders move to lock in profits, and the price action reverses
The Kospi has recovered part of the fall and is still well short of its peak
"It's now recovered about 20% from that bottom, but still stands substantially below its peak earlier this summer."
On refurbished phones, the forensic wipe and the one-year warranty are what separate a deal from a liability
Nguyen's cutoff: "not buy any phone that's older than two years old"
Malware is "relatively rare in the market", but a WSJ investigation found a victim who lost tens of thousands of dollars
What "Refurbished" Actually Buys You
The show opens on the trade-off in the secondhand market: "Buying a new phone might save you a few hundred dollars, but you could also be purchasing someone else's problems or something more sinister."
Moise frames the segment against the same shortage that runs through the second half of the episode — "as the price of new phones balloons from the memory chip crisis", a refurbished phone can be a good deal
Nguyen's definition of refurbished is physical work plus paperwork: the phone has been looked at, cleaned, repaired, and some of its parts may have been replaced
The step she says matters more is the data, not the hardware: "a forensic wipe of the phone to make sure that there are no lingering accounts that could prevent a cellular activation in the future or a lingering data that might inhibit your ability to use the phone"
The most common failure is an account, not a component: "if that phone is still on a Find My network associated with someone's Apple or a Google account, you can't activate it on a cellular network", and it cannot be transferred to the buyer
An unpaid phone is the next trap — if the previous owner never finished paying it off, "the carriers can block it from activating on US cellular networks"
Shoddy parts are the third: "maybe a reseller refurbished a phone with an aftermarket battery that's lower quality and doesn't last as long or it's not recognized by the system, and so you run into update issues", plus charging and headphone ports that do not work properly
Her fix is the seller, not the inspection: buy from the phone makers directly and from the wireless carriers, who "repair and renew models professionally"
The Warning Signs, and the One-Year Warranty Rule
Moise asks whether an average buyer can eyeball a bad repair or needs a third party to evaluate it
Nguyen answers with symptoms rather than diagnostics: "if that phone is running hot, if the battery drains really fast, if there are migration issues which could point to potential malware being installed on the device, stop using the phone and return it immediately"
The protection people skip is the warranty: "A lot of people don't pay enough attention to warranties when they're buying new phones."
Buying from the original manufacturer usually comes with "a one-year warranty, which is the gold standard"
"90 days is okay, but I'd say if you're buying a used phone, make sure it has a one-year warranty."
Malware Is Rare, and the Jury Duty Scam Shows What It Costs
Asked how worried buyers should be about malware or spyware, Nguyen points to reporting by her colleague Joe Barrett on a jury duty scam
The victim had recently bought a refurbished Samsung device that experts told the WSJ was likely loaded with malware
"It's a really scary scenario where she lost tens of thousands of dollars."
She puts the risk in proportion straight after: "Luckily though, malware is rare. I'm not saying it doesn't exist, but it's relatively rare in the market."
Buying directly from Apple, Samsung or Google, or from AT&T, Verizon or T-Mobile, means "there's a very good chance that your phone is not going to have any malware associated with it"
Seven Years of Updates, and a Two-Year Cutoff
"Every phone unfortunately has an expiration date." Nguyen says that is true of most modern technology
The support window is the real clock: "The more recent flagship devices are supported for seven years, and then after that they don't get security updates and software updates."
"My personal rule of thumb is to not buy any phone that's older than two years old."
The Rollerkospi, and the Two Chipmakers That Are the Index
The show sets the scale of the moves against Wall Street's: "On Wall Street, a 1% move in a major stock index like the Dow or the Nasdaq is enough to get investors' attention, but for the South Korean Kospi, that might be welcome news these days."
The nickname is the segment's premise: "The country's benchmark index has swung so wildly that investors have given it a new nickname, Rollerkospi."
The show's own figures on the run-up: "It was the world's top-performing stock market last year with a 76% gain", and "By mid-2026, its homegrown chip giants, Samsung Electronics and SK Hynix, accounted for more than 50% of the Kospi's value."
What broke it, in the show's framing: "AI stocks lost their footing as investors began to question whether enthusiasm pushed their stocks too far, too fast."
The Ants: Korea's Retail Investors, Borrowing to Juice the Bet
Moise opens the interview on the word ants, and Pitcher says it has become popular among South Korean individual investors
"It means they're weak individually, but capable of collective power, just like an ant colony."
It is the US meme-stock episode at national scale: what happened in the US a few years ago, when individual investors banded together on social media to buy specific stocks, was "a somewhat niche thing in the US that's gone very mainstream in South Korea"
The leverage is the part that made it dangerous: "It was like your grandmother investing in and buying the biggest companies, trying to make quick money, and also using more and more borrowed money to try and juice their bets."
A Severance Check Into the Index, and Half of It Gone in a Week
Asked which individual stories stuck with him, Pitcher says "So many people got involved in this and lost huge sums of money."
"This is a market that fell about 40% over six weeks earlier this summer."
The comparison he reaches for is 2008: "That's a huge drop equivalent with what the entire US market did over several years during the financial crisis just happening in a few weeks."
The case he leads with is a recently laid-off sound engineer with a big severance check: "He put his whole severance check, he said, into investments in the Korean index and he lost almost half of it just within a week."
The reporting turned up many like it — "people's money really evaporating at a much faster pace than they might've expected with the risk they thought they were taking on"
What Memory Buyers Are Betting On, and How a Rally Flips
Asked whether the damage spread beyond Korea, Pitcher says it did, then gives the background: Samsung Electronics and SK Hynix "both manufacture memory chips among other products"
The rally had a real earnings story underneath it. It started last year when chip makers focused on memory "started to see exploding demand for their product from data centers, from companies that are building out AI tools"
What a buyer is underwriting today: "people are betting on the fact that memory's going to stay in demand for a long time and profits are going to be huge, but things that rise very far, very fast, they often correct down"
The trigger is psychological rather than fundamental: “Something that’s been going up day after day and suddenly it falls 5%, a certain number of the people who have held and bought it might get spooked”
What they say to themselves, in Pitcher's telling: "I want to get out now. I want to lock in these profits."
"If everyone starts doing that at the same time, the price action can very quickly reverse in the opposite direction."
Buying the Korean Index Is Not Diversification
Moise asks what American AI investors should take from Korea, and Pitcher goes to the oldest advice there is: "A big thing with stock investing that people have preached for a very long time is diversification."
The usual reason to buy a country's whole index through a fund is precisely to get diversified exposure to stocks
In the US, individual companies swing hard, "But if you're buying the entire market in all these different companies, generally in the US, you've been fairly protected against massive swings" — the buyer is spread across industries and businesses
Korea's index does not work that way: "if you're just buying the Korean country index, it's really like you're making a bet on just a small handful of companies and you're exposed to that same volatility"
Where the Kospi Stands Now
Moise asks where the index sits as they speak, on the Thursday afternoon before the episode ran
"It bottomed towards the end of July and that 40% drawdown over a couple of months. It's now recovered about 20% from that bottom, but still stands substantially below its peak earlier this summer."
Pitcher's bottom line is that Korea showed what happens when a whole retail market buys one theme with borrowed money through an index that is really two companies, and that the same concentration is what American AI investors should check for in their own funds.
Products, Companies & Tools Mentioned
Samsung Electronics and SK Hynix (The two memory-chip makers whose exploding data-center demand drove the Kospi's run and which, on the show's figure, made up more than half the index's value by mid-2026)
Kospi (The South Korean benchmark at the center of the segment, nicknamed the Rollerkospi for the size of its swings)
Apple and Google accounts, and the Find My network (A lingering account tied to either one is the most common reason a secondhand phone cannot be activated on a cellular network)
AT&T, Verizon and T-Mobile (The carriers Nguyen names alongside the manufacturers as safe places to buy refurbished, because they repair and renew models professionally — and the carriers that can block a phone the previous owner never paid off)
Samsung refurbished handsets (The device type in the jury duty scam Nguyen cites, which experts said was likely loaded with malware)
The Dow and the Nasdaq (The show's reference point for a 1% move being enough to get attention, against the Kospi's swings)
Books & Resources Mentioned
Joe Barrett's WSJ investigation into a jury duty scam (Nguyen's colleague's reporting on a woman who bought a refurbished Samsung device and lost tens of thousands of dollars)
Jack Pitcher's WSJ story on the Kospi and Korea's individual investors (The reporting the second half of the episode is drawn from, including the interviews with retail investors)
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