I made $100,000 avoiding this common ETF investing mistake | Charlie Munger

The speaker begins by highlighting how intelligent investors often make costly mistakes with ETFs despite feeling smart about their choices. The first major mistake involves fund overlap - many investors buy multiple ETFs like QQQ, VGT, and VTI without realizing they're essentially buying the same companies multiple times. For example, 93% of QQQ's holdings are already in VTI, and there's roughly 50% portfolio weight overlap between QQQ and VGT, meaning investors pay multiple expense ratios for the same exposure. The speaker argues that overlap itself isn't inherently bad if it's deliberate and based on conviction about specific companies, but most investors do it accidentally. The second mistake concerns diversification, which the speaker calls 'a hedge against ignorance' rather than a virtue. They present data showing that over the past decade, international stocks (VXUS) returned only 3.7% annually and bonds (BND) just 1.3%, while U.S. stocks delivered 12-13% and technology nearly 20%. The speaker argues that spreading investments across multiple asset classes often dilutes returns from your best ideas rather than providing meaningful protection. The third and most serious mistake is constantly changing portfolios based on new information, emotions, or market events. The speaker emphasizes that being right over decades requires different behavior than being right today - it demands patience and the ability to sit still through volatility. They argue that frequent changes result in paying taxes on gains, resetting cost basis, and missing market time, ultimately eating into returns. The speaker concludes by advocating for building a foundation rather than a collection - owning 3-5 well-understood positions held through everything, rather than constantly optimizing. They stress that boring, patient investing typically outperforms exciting, active management.