You know what's wild? One of the biggest investing blunders in recent memory came from the guy who literally wrote the book on how not to make investing blunders. Warren Buffett's entire playbook was built on holding quality companies for decades, but somehow he managed to flip TSMC in less than a year—and it's cost Berkshire Hathaway something like $16 billion in unrealized gains.

Let me back up. Under Buffett's leadership, Berkshire Hathaway's Class A shares returned nearly 6,100,000% cumulatively. That's not a typo. The man built a trillion-dollar company by sticking to a few core principles that actually make sense when you think about them. Long-term thinking. Buying quality at reasonable prices. Owning companies with real competitive advantages and strong management. Capital returns to shareholders. Simple stuff, but apparently harder to execute than it looks.

Here's where it gets interesting. In Q3 2022, right in the middle of a bear market when things were actually reasonably priced, Buffett's team loaded up on Taiwan Semiconductor Manufacturing. We're talking 60 million shares for about $4.12 billion. TSMC was perfectly positioned for the AI boom—they make the chips that power everything from Apple to Nvidia. It was a textbook Warren Buffett move at first glance.

But then something shifted. By Q4 2022, Berkshire had already dumped 86% of the position. By Q1 2023, they were completely out. The entire trade lasted maybe five to nine months. When analysts asked Buffett why, he basically said he didn't like TSMC's location and had reconsidered. Probably worried about export restrictions to China or geopolitical risks. Fair concerns, maybe. Terrible timing though.

Because here's the thing—the moment Buffett bailed, demand for AI chips went absolutely nuts. TSMC's capacity couldn't keep up. The company's growth accelerated hard, and the stock reflected that. By July 2025, TSMC joined the trillion-dollar club. If Berkshire had just held that initial position without selling a single share, it would be worth close to $20 billion right now. Instead, they walked away with maybe $4 billion in gains, leaving $16 billion on the table.

It's honestly the most Warren Buffett thing ever—a master investor breaking his own rules and paying for it. Makes you think about what his successor, Greg Abel, is going to do differently. Probably stick to the basics and actually hold companies for more than nine months.