Last month, U.S. News & World Report published an article that we think was as dangerous as it was dumb. Titled "3 Reasons You Should Not Manage Your Own Money," the thesis was that investing, you know, is really hard and therefore best kept to professionals.

You may not be surprised to know that the article was written by one of those very professionals, one Kelly Campbell of Campbell Wealth Management, who, if you live near Fairfax, Va., would probably love for you to take his advice and hire him. But before you run out and do that, let's at least consider the reasonableness of his reasons.

Reason No. 1: The financial world has changed.
According to Mr. Campbell, the "practice of buying stock in a company you like, or one that manufactures the products you use, doesn't work like it used to. The markets move too quickly. ... As a result, it's harder to make money by buying and selling at the right time."

We agree that market timing is a loser's game today, but here's a news flash: It's always been that way. Business school professor Javier Estrada provides some of the most compelling evidence of this. After studying data from 15 global markets over 70 years, Professor Estrada concluded that "less than 0.1% of the days considered" actually matter to long-term returns, meaning "the odds against successful market timing are staggering."

This is more than 70 years worth of data! All of which goes to show: You should not try to time the market today any more than you should've tried to time it 10 or 20 years ago. Furthermore, you shouldn't entrust your wealth to someone who seems to imply that he can time the market.

And as for companies that make products you like? We agree it's a simplistic investing philosophy. But sometimes it's helpful to keep things simple.

So long as you were able to tolerate volatility and try not to time the market, household brands Coca-Cola (NYSE: KO) and Nike (NYSE: NKE) would have earned you 32% and 351%, respectively, over the past decade. They wouldn't have done this because you use their products, but the fact is, great companies will perform provided you give them the time to do so -- and we suspect both of these great companies will perform well over the next decade given that they're just getting started selling their products in the emerging world.

Reason No. 2: The average investor does not have the necessary time, tools, or inclination to research and monitor their portfolio accurately.
The bias here is that an investor can only be successful by winning the same short-term game that many so-called professionals try to play on a daily basis, trading in and out of hedged positions based on metrics such as momentum ... that don't have anything to do with the performance of a good business over a long period of time.

So, yes, we agree that investors who try to play that game are likely to lose. We don't have the same computing power, nor do we have an army of Ph.D.s working on our behalf, as a firm like Renaissance Technologies (who can win at this game) does. The solution is not to concede defeat and hand money to a professional who in most cases also does not have the same resources or smarts as Renaissance. The solution is to avoid playing that short-term game.

The fancy term for this is "time arbitrage," but it's as simple as buying great companies or low-cost indexes at good prices, and then holding them for the long term.

Reason No. 3: The average investor does not have access to certain investments that could significantly improve their returns and lessen their risk.
This is the most inane reason of all. Was Mr. Campbell putting his clients in the senior tranches of collateralized debt obligations (CDOs) built from residential mortgages? Those "sophisticated" products were advertised to investors as being safe, but, as we found out during the recent financial crisis, they turned out to be anything but.

The key to successful investing is not to make it more complicated. As it gets more complicated, you end up with a portfolio that has a lot more things you don't know you don't know -- a situation that toppled even the financial whizzes at AIG, Lehman, Bear, and others.

Our alternative advice? Keep it simple. Figure out what your financial goals are (retirement, education, etc.). Determine how much you need to save and what return you need to achieve, and then allocate your assets to plain-vanilla stocks and bonds to do just that. The fabulous low-cost indexes offered by Vanguard are one way. Vanguard Total Stock Market (NYSE: VTI), for example, is a great place to keep your equity investments, and not coincidentally is long a lot of companies -- Coca-Cola, Nike, and more -- whose products you use.

If you want to pick some stocks on top of a low-cost index approach and are prepared to put in the due diligence, we say go ahead. We think you'll actually do quite well by thinking long term, sticking with great companies, and avoiding the fees that so many professionals charge. As another academic paper, "Assessing the Costs and Benefits of Brokers in the Mutual Fund Industry," concluded:

We find that the brokered channel sells funds with inferior pre-distribution-fee returns. The channel does not show any evidence of superior aggregate market timing ability, and shows the same return-chasing behavior as observed among direct-channel funds. Finally, more sales are directed to funds whose distribution fees are richer.

It's OK to be an amateur
Indignation aside, we disagree with the notion that non-professional investors are incapable of managing their own money. It's not that we're biased against all professional money managers -- many act as fiduciaries and help build wealth for their clients. In fact, if you need some help figuring out your financial goals and determining your required savings rate and required rate of return to achieve, a consultation with a fee-only financial planner could well be in your best interest. But don't let any wealth manager tell you that you can't do it yourself.

If Mr. Campbell had wanted to give good advice to U.S. News & World Report readers, his default guidance should not have been to "hire a professional," but rather to get a plan and "buy an index fund." We think that's just fine for 90% of the people out there, but the Fool is also founded upon the belief that for people who want to learn, talk with others, share ideas, and research businesses, it's possible to outperform the market.

You can situate yourself for next year with our new free report, "Motley Fool Top Picks and Perspectives 2011," by entering your email address in the box below. You'll also hear about our Million Dollar Portfolio service, which features best-of-breed stock picks from the Fool's advisory services.

Fool.com managing editor and one-time U.S. News intern Brian Richards does not own shares of any companies mentioned. Global Gains and Million Dollar Portfolio associate advisor Tim Hanson doesn't, either. Coca-Cola is an Inside Value and Income Investor selection. Nike is a Stock Advisor pick. The Fool owns shares of Coca-Cola. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.