One Year After 0407: How Many Cognitive Biases Did You Fall For During the Crash?

On April 7, 2025, Taiwan's TAIEX dropped 2,065 points in a single day — the largest point decline in its history. In those 72 hours, many Taiwanese investors made the most expensive decisions of their investing careers. Some panic-sold. Some were forced out by margin calls. Some sold and regretted it. Some held on but have been anxious about markets ever since.

One year later, the 0050 ETF is up over 47%, and margin lending balances have surged past NT$3,500 billion to multi-year highs. It's as if nothing happened. But the results of the U.S. Section 301 investigation are expected around July 2026. The next bout of volatility isn't a question of "if" — it's a question of "when."

This article has one purpose: before the next crash, figure out what psychological mistakes you made during the last one.

TL;DR

• April 7, 2025 was the TAIEX's largest single-day drop ever — 18.3% decline over three days, 1,700+ stocks hitting limit down simultaneously
• Behavioral finance research identifies 7 cognitive biases that get amplified during market crashes, all of which played out in real time during 0407
• Taiwanese retail investors' disposition effect (holding losers too long) reverses during crashes into mass selling at the worst possible moment
• Use the "0407 Mirror Test" — 7 questions to identify your dominant bias type
• July 2026 presents a concrete tariff-related volatility window; now is the time to build your playbook

What Actually Happened in Those 72 Hours

Let's reconstruct the timeline, because memory is unreliable.

On April 2, 2025, Trump announced "Liberation Day" tariffs, slapping a 32% reciprocal tariff on Taiwan. The problem: Taiwan was on Qingming (Tomb Sweeping Day) holiday. For four days, global markets tanked while Taiwanese investors could only watch from the sidelines, helpless. Panic fermented in group chats and social media, with no way to act.

April 7 opened, and four days of pressure released all at once.

The TAIEX fell 2,065 points (-9.70%), closing at 19,232. Over 1,700 stocks hit their daily limit down. TSMC hit limit down for the first time in its 30-year listing history. Over the following three days, the TAIEX shed a total of 3,906 points — an 18.3% decline that exceeded the combined drops of the 2008 financial crisis and the 2020 COVID crash.

But the truly brutal part wasn't the index. It was the margin lending.

In four days, NT$750 billion in margin lending was wiped out — a 25% evaporation of total margin balances. On April 9 alone, NT$330 billion in margin calls were issued. What does this mean? It means a massive number of retail investors didn't "decide" to sell — they were forced to sell. When the broker's margin call lands, you either deposit more cash or your positions get liquidated. No negotiation.

Meanwhile, foreign institutional investors were net buyers on April 7. Retail was panic selling. Institutions were picking up the shares.

This wasn't a coincidence. It was a systematic behavioral divergence — and understanding it is what this article is about.

The 7 Cognitive Biases, 0407 Edition

Behavioral finance isn't new. But most people have only encountered these concepts in textbooks. April 7, 2025 offers something rare: a real-time case study of every major cognitive bias, played out by real Taiwanese investors with real money.

Each bias below follows the same structure: what it is, how it manifested on 0407, and a question for you to answer honestly.

1. Herd Behavior: Was Your Sell Decision Yours, or the Market's?

What it is: During a market decline, investment decisions get driven by what others are doing rather than your own independent analysis.

How it showed up on 0407: The margin call cascade created a chain reaction. Stop-loss orders, ETF rebalancing mechanisms, margin calls, and private lending capital withdrawals — all four triggered simultaneously, dragging even investors who wanted to hold into the selling pressure. Group chats were flooded with "get out now" messages. Many sell decisions were the product of emotional contagion, not analysis.

Ask yourself: Was your sell decision on 4/7 something you initiated, or did you make it after seeing group chat messages and margin call notices? If you had no margin exposure and weren't checking any group chats, would your decision have been different?

2. Loss Aversion: Losses Hurt 2.5x More Than Gains Feel Good

What it is: Prospect Theory in behavioral economics shows that the psychological pain of a loss is roughly 2 to 2.5 times the pleasure of an equivalent gain. This isn't a personality flaw — it's how the human brain is wired.

How it showed up on 0407: Loss aversion produced two completely opposite failure modes simultaneously. First, some investors refused to cut losses on positions where the investment thesis had clearly changed, holding through the crash and suffering even deeper losses before being forced out. Second, some investors couldn't bear the pain in the moment and dumped their entire portfolios — including positions with perfectly intact fundamentals.

Ask yourself: Before 0407, did you have any positions where you knew the thesis had changed but couldn't bring yourself to take the loss? The stocks you sold during the crash — looking back now, do you regret it?

3. Disposition Effect: The Hidden Landmine for Taiwanese Investors

What it is: Investors tend to sell winners too early (locking in the pleasure of gains) while holding losers too long (avoiding the pain of confirming a loss). Academic research shows that Taiwanese retail investors exhibit the disposition effect at roughly 2.5 times the severity of American investors.

How it showed up on 0407: This is the most counterintuitive part. Under normal market conditions, Taiwanese retail investors don't sell losing stocks — that's the textbook disposition effect. But when a crash hits and psychological pain crosses a threshold, the same investors dump all their losing positions at once, at the worst possible moment. The disposition effect makes you "not stop-loss" in normal times, then "stop-loss at the absolute bottom" during a crash.

Ask yourself: In the week before the crash, what percentage of your portfolio was underwater? Did you have stop-loss rules in place, or were you waiting for positions to recover?

4. The Overconfidence Paradox: The More You Know, the Harder You Might Fall

This might be the most counterintuitive of all seven biases.

What it is: A study of approximately 190,000 investors (PLoS One, 2024) found a paradox: each unit increase in financial literacy reduced panic selling probability by 2.4%. Sounds reasonable. But each unit increase in overconfidence increased panic selling probability by 1.2%. The problem? Highly financially literate people tend to be the most overconfident.

How it showed up on 0407: Investors who were using margin before 0407 were often the "most confident" participants in the market. They had built up conviction during the 2023-2024 AI bull run, believing they truly understood the market. But how much of that confidence came from genuine skill, and how much from the luck of being in a bull market? When the 32% tariff hit, their overconfidence had led them to take on leverage beyond their actual risk tolerance, and they were forced to liquidate at the worst moment.

Ask yourself: Did you have margin exposure before 0407? Was your confidence in your own judgment based on analytical skill, or on the fact that you'd been making money for two years straight?

5. Recency Bias: Your Memory Is Making Decisions for You

What it is: The human brain overweights recent events when predicting the future.

How it showed up on 0407 — both sides: Before the crash, recency bias made you underestimate risk. The 2023-2024 bull market memory was so powerful that "markets go up" felt like a law of nature, and warning signals were automatically filtered out. After the crash, recency bias flipped: the pain of 0407 was so vivid that many investors stayed underweight equities or held excessive cash even as the market rebounded — watching the 0050 ETF climb 47% without them.

Ask yourself: In the three months after 0407, did your equity allocation decrease significantly? Looking back, what impact did that adjustment have on your annual returns?

6. Hindsight Bias: No, You Didn't "See It Coming"

What it is: After an event, people systematically overestimate their ability to have predicted it, believing they "knew all along."

How it showed up on 0407: Trump's tariff announcement came on April 2. There were four full days during the Qingming holiday to think and take protective action. But the number of investors who actually made concrete hedging moves between April 3-6 was vanishingly small. Yet after the crash, many people claim they "had a feeling."

The danger of hindsight bias isn't just flattering your past self. It's worse than that: it makes you overestimate your ability to predict the next crash. "Because I went through 0407," some investors think they'll time the next downturn better, leading to an endless wait for a "better entry point" — while missing a 50% rally over the past year.

Ask yourself: Between April 3-6, did you take any concrete protective action? If the answer is no, but you now feel like you "knew it was coming," what does that gap tell you?

7. Confirmation Bias: You Only See What You Want to See

What it is: Investors spend roughly 80% of their time consuming information that confirms their existing positions.

How it showed up on 0407: Q1 2025 was the peak of the AI bull market. Bullish analysis on TSMC and AI stocks dominated every media channel and social platform. If your information diet at the time was entirely bullish, that wasn't because bearish signals didn't exist — it was because your brain was systematically filtering them out.

Ask yourself: Before 0407, can you name three analysts or sources that were publicly bearish on Taiwan's stock market in Q1 2025? Did you actively seek out viewpoints that contradicted your portfolio positions?

The 0407 Mirror Test: Find Your Dominant Bias

Here are the 7 self-diagnostic questions in one table. Answer honestly — this is for you, not for anyone else.

Dimension	Question	Corresponding Bias
Decision trigger	Was my sell decision on 4/7 self-initiated or market-forced?	Herd behavior
Pre-crash portfolio	What % of my positions were underwater with no stop-loss?	Disposition effect
Leverage audit	Did I have margin before 0407? Was my confidence skill or luck?	Overconfidence
Information sources	Can I name 3 bearish sources from Q1 2025?	Confirmation bias
Post-crash action	How did my equity allocation change in the 3 months after 0407?	Recency bias
Prediction audit	Did I take any action between April 3-6?	Hindsight bias
One-year scorecard	Did my returns beat 0050's +47% in the year after 0407?	Combined result

If you found issues in three or more dimensions, don't beat yourself up. These biases are standard equipment in the human brain, not personal defects. What matters is that you now know they exist.

July 2026: The Next Volatility Window — Are You Ready This Time?

Now let's look forward.

The risk ahead isn't hypothetical — it has specific dates. The U.S. launched a Section 301 investigation in March 2026, targeting Taiwan's semiconductor and electronics industries. Under the statutory timeline, results are expected within 150 days — around July 2026. At the same time, Section 122 tariff measures are set to expire. Two risk windows overlapping. This is a volatility point you can mark on your calendar.

I'm not predicting a crash. No one can. But what I am doing is this: while I'm still thinking clearly, setting rules in advance so that when the time comes, I don't need to "make decisions."

5 Rules That Don't Depend on Emotions:

1. Decide your maximum tolerable drawdown first. In calm markets, figure out how much your portfolio can drop before it affects your life. Don't make any other decisions before setting this number.

2. Set automatic stop-losses on margin and leveraged positions. Don't leave yourself in a position where you have to "decide" whether to close during a crash. April 7 showed us that decisions made in that moment are almost always wrong. Let rules execute for you.

3. Build an information diet. Your sources should include at least one voice that disagrees with your portfolio thesis. Not because they're necessarily right, but because you need opposing viewpoints to calibrate your own.

4. Write down your playbook. Take a piece of paper and write: "If the TAIEX drops more than X% due to tariff news in July, my plan is ______." Write it now, not when it's happening. Behavioral science calls this "pre-commitment," and it works far better than you'd expect.

5. Enforce a 48-hour cooling period after a crash. The 0407 margin calls didn't give people time to cool down. But if you don't have margin exposure, you actually have time. Set a rule: if the market drops more than 5% in a single day, make no non-automated trades for 48 hours.

The common thread across all five rules: move the decision from "during the crash" to "right now." Because the version of you sitting here today is rational. The version of you during the next crash won't be.

Risk Disclosure

This article is financial education content, not investment advice, and does not constitute any buy or sell recommendation.

Recognizing your behavioral biases is only the first step. Knowing they exist doesn't guarantee you'll avoid them next time, but it does let you build mechanisms to reduce their impact.

Markets don't always bounce back in a V-shape. The +47% return in the year after 0407 is a result, not a rule. Holding is itself a decision that carries risk — don't assume the next time will play out the same way.

Conclusion

April 7, 2025 wasn't some anomaly unique to Taiwan's stock market. It was a live demonstration of every cognitive bias in the behavioral finance textbook. Herd behavior, loss aversion, the disposition effect, overconfidence, recency bias, hindsight bias, confirmation bias — all seven performed their full routine within 72 hours.

One year later, most people have chosen to forget, or worse, used hindsight bias to re-edit their memories, believing they'll "handle it better next time." But margin lending balances hitting multi-year highs tell us that collective market memory is fading and overconfidence is rebuilding.

The July 2026 tariff window is straight ahead.

Take the "0407 Mirror Test" now. Not to regret past decisions, but so that the next time you're sitting in front of your screen watching the TAIEX plunge, you can open the playbook you wrote in advance and execute it.

In that moment, you won't need stronger nerves. You'll need a system that doesn't require nerves at all.