(FORTUNE Magazine) – Mutual funds reporters lead a secret investing life. By day we write "Six Funds to Buy NOW!" We seem to delight in dangerous sectors like technology. We appear fascinated with one-week returns. By night, however, we invest in sensible index funds.

I know, because I once was one of those reporters--condemned to write a new fund story every day--when I covered funds for an online publication. I was ignorant. My only personal experience had been bumbling into a load fund until a colleague steered me to an S&P 500 index fund. I worried I'd misdirect readers, but I was assured that in personal-finance journalism it doesn't matter if the advice turns out to be right, as long as it's logical. You're supposed to produce the most stories "that end in investment decisions," so publications substitute formulas for wisdom. The formula for recommending funds: Filter according to returns, then add something trendy--high tech, no tech, whatever. For an extra twist, omit funds with loads or new managers.

The problem is that recent returns, whether from one week or the old standby three years, don't predict future results. Nothing predicts future results. The best you can do is to hold on to low-cost, diversified funds and be oblivious to short-term static.

We did tell people that. But we were preaching buy-and-hold marriage while implicitly endorsing hot-fund promiscuity. The better we understood the industry, the sillier our stories seemed. When a certain colleague would see a rival publication with its obligatory SIX FUNDS TO BUY NOW! headline, he would slap the magazine down on his desk and protest with feigned jealousy, "We were scooped! They stole our story!"

After months of interviewing managers and studying statistics and strategies, I made only one move in my own retirement portfolio--into my fund family's more diversified index fund. The fund reporters I knew came secretly to favor low-cost index funds. The fund family I adopted has particularly low fees and a good reputation. That's not to say that other groups are bad. Many educate their shareholders, keep expenses low, and get people into the market. But most actively managed funds can't justify their existence beyond that.

Unfortunately, rational, pro-index-fund stories don't sell magazines, cause hits on Websites, or boost Nielsen ratings. So rest assured: You'll keep on seeing those enticing but worthless SIX FUNDS TO BUY NOW! headlines as long as there are personal-finance media.

--One anonymous FORTUNE writer