So I've been thinking about one of the most interesting investing blunders in recent memory, and it involves Warren Buffett in a way that doesn't get talked about enough. The man built Berkshire Hathaway into a powerhouse through decades of discipline and patience, but a five to nine month fling with Taiwan Semiconductor Manufacturing (TSMC) just cost his company something like $16 billion in unrealized gains. Yeah, you read that right.

Here's what happened. Back in Q3 2022, when markets were getting hammered, Warren Buffett and his team spotted what looked like a solid opportunity. They loaded up on TSMC - we're talking about $4.12 billion and over 60 million shares. At the time, it made sense on paper. TSMC was the world's leading chip fabricator, supplying advanced chips to Apple, Nvidia, and basically every major semiconductor player. Plus, the company was positioned right at the center of the AI boom with its advanced CoWoS technology. For someone like Buffett, who's built his reputation on long-term thinking, this should have been exactly the kind of position he'd hold for years.

But then something shifted. By Q4 2022, Berkshire started selling. They dumped 86% of the stake that same quarter and completely exited by early 2023. When analysts asked Warren Buffett about it in May 2023, he basically said he didn't like TSMC's location and had reevaluated. The reasoning pointed to geopolitical concerns - the CHIPS Act, potential export restrictions to China, all that stuff.

The problem? His timing couldn't have been worse. TSMC ended up being absolutely essential to the AI infrastructure buildout. Nvidia's GPU demand went insane, backlogs piled up, and TSMC kept expanding capacity. The stock just kept climbing. Fast forward to July 2025, and TSMC joined the trillion-dollar club. If Warren Buffett had just held that initial position without selling a single share, it would be worth almost $20 billion by now.

What makes this interesting isn't just the dollar amount - it's that it violated one of Warren Buffett's core principles. He's always preached long-term thinking, buying quality businesses and letting them compound over decades. But this time, he made a short-term trade based on what looked like a reasonable concern at the moment. Geopolitical risk is real, but he didn't give the underlying business enough time to prove itself through that uncertainty.

It's a reminder that even the best investors can make calls that look smart in the moment but turn out to be expensive in hindsight. The difference is that when you're managing hundreds of billions in assets like Berkshire does, even a rare mistake gets magnified into something massive. With Greg Abel now running the show, I'd expect Berkshire to lean harder into those time-tested principles that made Warren Buffett legendary in the first place.