ETF Mistakes Investors Make With 'Set It and Forget It' Funds — Concentration Risk

One recurring issue with "set it and forget it" ETF strategies is the misconception that owning more funds automatically delivers better diversification. Investors often select funds based on name or past returns rather than examining the underlying holdings, which determine true exposure and risk.

The problem typically appears in two ways: concentration in a handful of large stocks through sector-heavy ETFs and overlap among multiple funds that hold largely the same positions. For example, technology-focused ETFs such as Invesco QQQ have become top-heavy following the recent rally of the so-called "Magnificent Seven," and comparisons show significant overlap between popular broad-market ETFs like Vanguard's VOO and VTI. Reports note that a small group of mega-cap names can represent a very large share of certain indices, increasing downside risk if those names stumble.

These dynamics influence market outcomes and investor returns. Concentration and overlap mean that apparently diversified portfolios can fall in lockstep during market corrections, reducing the protective value of diversification. Investors who skip periodic rebalancing may find their target allocations—such as a 70/30 stocks-to-bonds mix—drift materially after strong equity runs, unintentionally elevating portfolio volatility and drawdown potential.

In the broader context, the ETF industry's proliferation of low-cost, thematic, and niche products has expanded investor choice but also increased the need for due diligence. Easy access to tailored exposures invites momentum-driven allocation decisions that can concentrate risk. Passive vehicles have benefits, yet they do not eliminate the need for portfolio governance and occasional review to ensure alignment with long-term objectives.

Market practitioners recommend straightforward mitigants: periodically inspect fund holdings and sector weights, avoid redundant funds with high overlap, and adopt rules-based rebalancing to maintain intended asset mixes. These steps allow investors to keep the simplicity of a largely passive approach while addressing hidden concentration and overlap risks that can erode long-term outcomes.