Money Guy Show
Money Guy Show

The Biggest DIY Investing Mistakes

October 2, 2026

AI Summary

5 min read

When a family member asked financial advisor Brian Preston to review their 401(k) at a holiday gathering, he asked how they had chosen the funds. The answer: "Every fund that had 'growth' in it, I chose." That single moment captures the core tension of do-it-yourself investing—good intentions and a reasonable-sounding heuristic can lead to a portfolio that is anything but diversified. In this episode of The Money Guy Show, Preston and co-host Bo Hanson walk through seven common mistakes they have observed over decades of working with investors, explaining the psychology behind each error and offering concrete fixes. Their stance is not anti-DIY; they launched the show in 2006 precisely to help people who could not afford a financial advisor. But they argue that as complexity and account balances grow, the same DIY habits that worked early on can quietly sabotage long-term results.

The Illusion of Diversification

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What you'll learn

  • 1 (01:30) **Introduction: Why This Episode Matters for DIY Investors** - The hosts clarify they are not anti-DIY; they created the show in 2006 to empower people who can't afford an advisor. They note that 64% of workers now manage their own finances, often relying on family, online research, or even AI.
  • 2 (04:37) **Mistake #1: Too Many Overlapping Funds** - A common error is buying multiple funds with "growth" in the name, not realizing the top holdings are nearly identical, creating a false sense of diversification.
  • 3 (08:19) **Mistake #2: Ignoring Asset Location** - It's not just *what* you own, but *where* you own it. Choosing the wrong account type for an investment creates a "tax drag" that silently erodes returns.
  • 4 (14:07) **Mistake #3: Not Managing Risk Realistically** - Investors are driven by fear and greed, leading to two extremes: being too aggressive (no time to recover from a crash) or too conservative (being eaten alive by inflation).
  • 5 (19:28) **Mistake #4: Forgetting to Update Beneficiaries** - A terrifying statistic: only 36% of parents have designated beneficiaries on their retirement and life insurance accounts, meaning assets may not go to the intended people.
  • 6 (23:49) **Mistake #5: Losing Track of Your Investments** - There are 31.9 million "lost" 401k accounts in the U.S., holding over $2 trillion in forgotten savings. The average worker changes jobs 12 times, making it easy to leave assets behind.
  • 7 (27:42) **Mistake #6: Trying to Time the Market** - Even though everyone knows it's a mistake, emotional panic during downturns leads investors to "cry uncle" and sell at the worst possible moment, locking in losses and missing the recovery.

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Guests on this episode

Show Notes

DIY investing can be a powerful way to build wealth—but even experienced investors can make costly portfolio mistakes. Brian and Bo break down 7 common investing mistakes, including overlapping index funds and ETFs, poor asset location between Roth IRAs, 401(k)s and brokerage accounts, taking the wrong amount of investment risk, forgotten retirement accounts, outdated beneficiaries and trying to time the stock market. You’ll learn how diversification, tax-efficient investing, portfolio rebalancing, dollar-cost averaging and smarter retirement planning can help you build a more intentional investment strategy—and how to recognize when your financial life may be getting too complex to manage alone.


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