These ETF mistakes can ‘quietly erode long-term returns,’ advisor says

The exchange-traded fund (ETF) market has expanded significantly, surpassing $11 trillion with substantial recent inflows, as investors seek lower-cost and tax-efficient options. Despite this growth, financial experts caution that many investors are making common mistakes that could detrimentally impact long-term returns, such as chasing performance, trend-hopping into volatile thematic funds, and overlooking critical expense ratios. With regulatory decisions potentially leading to an even greater proliferation of ETF products, understanding these pitfalls is crucial for institutional investors navigating the evolving market landscape.

Analysis

The exchange-traded fund (ETF) market has expanded significantly, now exceeding $11 trillion with substantial inflows of $511 billion in the first half of 2025, driven by investor demand for lower-cost, tax-efficient options. This growth is poised to accelerate further following U.S. SEC regulatory decisions in late September, which could introduce new ETF share classes for mutual funds. This regulatory shift is expected to increase product proliferation and market complexity.

Despite robust market expansion, financial experts highlight critical investor mistakes that could erode long-term returns. Common pitfalls include "chasing performance" or "herd mentality" into rising assets, and "trend hopping" into volatile, narrowly focused thematic ETFs like AI or crypto. These behaviors often lead to buying at peaks and selling during declines, undermining diversification benefits.

A significant oversight is the failure to scrutinize ETF expense ratios, with many investors unknowingly paying higher fees for identical index exposure, such as the S&P 500. While broad market index ETFs can have expense ratios under 0.05%, higher costs, even seemingly small, can significantly drag on returns over time. This fee sensitivity becomes increasingly important as the market expands.

Key Decisions for Investors

• Investors should critically evaluate ETF selections beyond past performance, ensuring alignment with long-term financial goals rather than succumbing to "herd mentality" or "trend hopping" into volatile thematic funds.
• Conduct thorough due diligence on expense ratios for all ETF holdings, particularly for broad market indices, to minimize fee drag and optimize net returns over time.
• Monitor the impact of recent SEC regulatory decisions, as the anticipated influx of new ETF share classes could introduce both opportunities and increased complexity in product selection and portfolio construction.