Bill Gates revealed his biggest investment regret—and it's a mistake most people

“The biggest mistakes are the ones that never show up on your balance sheet … the deals you knew enough to do but sat there sucking your thumb.” — Warren Buffett

“I wish we’d kept that 5-percent stake in Apple. Selling it was—well—pretty foolish.” — Bill Gates (2025 interview for his memoir Source Code)

When two of the richest brains on the planet admit to billion-dollar blunders, it pays to listen. In a free-wheeling Q&A at the University of Nebraska back in 2005—captured on YouTube as “Warren Buffett and Bill Gates: Go Back to School”—students asked the obvious: What’s the worst investment you’ve ever made?

Buffett laughed and said, “How long do you have?” Gates, for his part, pointed to the deals Microsoft missed—especially search—and decisions they made too early, like betting on IPTV years before the bandwidth existed. The sub-text was clear: both men suffered from selling winners too soon or hesitating on obvious opportunities.

And that, friends, is exactly the trap retail investors fall into every single day.

1. Gates’ $150 million Apple “oops”

In 1997 Microsoft threw Apple a $150 million life-line. By 2003 the stake was sold for a tidy $550 million. Not bad—except that same slice would be worth roughly $184 billion today. In a February-2025 Axios press blitz, Gates called winding down that position “foolish, foolish.”

Why he sold: Microsoft had quadrupled its money, Steve Jobs looked wobbly, and antitrust lawyers were circling Redmond. Locking in a win felt prudent. Hindsight shows it was the textbook definition of the disposition effect—the bias that nudges us to cash out winners prematurely and ride losers far too long.

Behaviour-finance researchers first documented the effect in the 1980s and it has been confirmed in brokerage data ever since.

2. Buffett’s invisible losses

Buffett told the students he loses zero sleep over dud stocks he did buy; the real agony is the 10-digit profits he left on the table by waiting on obvious calls—omission not commission . Classic examples include passing on Google in 2004 and Netflix in 2007. The numbers never scar Berkshire’s statements, but the opportunity cost is astronomical.

“I was sucking my thumb when I should have been writing checks.” — Buffett

Sound familiar? Most of us trim a high-flyer because “25 percent feels good,” then freeze when a dud drifts lower because selling would prove we were wrong.

3. Why our brains love short-term certainty

• Loss aversion: neurologically, a $1 loss hurts roughly twice as much as a $1 gain feels good.

• Mental accounting: we lock in the “win” to bank a dopamine hit and quarantine the potential regret.

• Attention bias: gains are vivid; opportunity cost is invisible.

Academic studies show individual traders sell winners 50 percent more often than losers, even though the sold winners go on to outperform the clunkers they keep. Gates’ Apple exit and Buffett’s “thumb-sucking” are the billionaire-scale versions of the same twitch.

4. How to stop repeating their mistake

Gates himself keeps a “Think Week” twice a year—no meetings, just reading, white-boarding, and asking: Is our roadmap missing the next big thing? Copy that discipline: block two days a year to step back from screens and sanity-check your portfolio against secular trends, not this week’s CPI print.

5. The upside of not touching your winners

Had Microsoft simply held the Apple stake—and done nothing else—the stock would now equal nearly half of its own $400-billion cash pile. The mistake didn’t sink the company, but consider what compounding could do for your own retirement account. A $10,000 position that 20-bags over 20 years is life-changing, but only if you let it.

Buffett frames it perfectly:

“Someone is sitting in the shade today because someone planted a tree a long time ago.”

Plant more trees and stop uprooting the healthy ones just to admire the roots.

6. Key takeaways you can use tomorrow morning

1. Separate decision from emotion.
   If the urge to sell appears, write down why in one line and sleep on it. Feeling “uneasy” isn’t a thesis.

2. Benchmark against your own timeline, not the market tape.
   Gates sold Apple because four years felt like forever; in venture-scale tech, that was the first inning.

3. Reward patience, not activity.
   Check your broker once a week, not 12 times a day. Data from 10,000 discount-broker accounts shows lower-frequency traders earn higher net returns

4. Treat cash as dry powder, not a trophy.
   Buffett keeps $100 billion idle because it’s optionality, not bragging rights. If you sell a winner, have the next idea ready.

5. Don’t confuse action with progress.
   The average U.S. equity mutual fund turns over 63 percent of its positions annually. Berkshire’s average holding period is 8-plus years.

Final word

Bill Gates and Warren Buffett have different operating systems—one hacks code, the other allocates capital—but both agree the deadliest investing mistake is psychological, not analytical. Gates’ $184-billion Apple “regret” and Buffett’s $10-billion “thumb-sucking” are megaphone warnings: let your winners run.

So the next time your favourite stock pops 30 percent and your finger twitches over the sell button, remember Gates’ rueful laugh and Buffett’s blunt truth. Then pour yourself a Blizzard, sit on your hands, and let compounding do the heavy lifting. Your future self will thank you.