Down, down, down the market goes. Where it stops, nobody knows. And who's to blame?

This week we can point our little fingers at Abby Joseph Cohen, the managing director and chair of the Investment Policy Committee of Goldman Sachs (NYSE: GS). On Tuesday, she announced a reduction in the stock allocation in Goldman Sachs' model portfolio from 70% to 65%.

"For the first time in a decade," the media-appointed leader of the bulls declared, "our model portfolio is no longer recommending an overweighted position in technology." Uh oh.

On the basis of this call, many investors charged out of technology stocks in a manner reminiscent of the famous Running of the Bulls in Pamplona, trying to avoid the goring of a potential bear market.

Who is Abby Joseph Cohen and who anointed her Prognosticator Extraordinaire?

Reuters calls her "one of Wall Street's most influential analysts." Louis Rukeyser calls her "the most influential market forecaster."

Her magic wand surpasses all others in making a prediction a reality. On the day after Ms. Cohen's allocation change, Morgan Stanley Dean Witter raised the equity portion of its balanced portfolio to 75 percent from 70 percent. But apparently, no one listened, or cared. The Nasdaq continued its free fall.

You'd think that with such a talent for market predictions, Ms. Cohen has had some training in the supernatural. Or at least some independent study with Nostradamus.

No, her training was rather traditional. After graduating with economics degrees from Cornell University (B.A.) and George Washington University (M.S.), she began her career as a research assistant at the Federal Reserve Board. Following that, she spent seven years at mutual fund company and Rule Maker holding T. Rowe Price (Nasdaq: TROW), after which she headed to Drexel Burnham Lambert. She stayed there for another seven years, until the company collapsed into bankruptcy resulting from a massive fraud case brought by the Justice Department (in which she had no involvement). After a short stint at Barclays de Zoete Wedd, she joined Goldman Sachs and has worked there ever since.

According to a Business Week profile of Ms. Cohen, her "chief claim to fame is that she has been bullish on the stock market ever since February, 1991, about three months after the Dow hit bottom at 2,365 and began its epic advance."

Ms. Cohen, however, is no psychic. Back in January 1998, she predicted that stock market returns would be closer to normal in 1998, as would stock price volatility. She projected "good, but not extraordinary, returns from U.S. equities following three years of abnormally large share price increases." She was wrong on that count, as 1998 closed with the S&P up 28.58%, the Nasdaq up 39.63%, and the Rule Breaker up 199.08%, throughout a year of high volatility.

Still, 1998 was one of the years that Ms. Cohen made her mark as she correctly advised her clients to remain in equities even as the market fell nearly 20% from July to October. This was similar to a call she made back in 1996, when she supported a bullish stance on equities, citing low inflation and rising earnings, while many of her colleagues were predicting the return of the big, bad bear.

By becoming the guru and symbol of the bull's great run, Ms. Cohen's recent move to a slightly more conservative position has shaken the ground from under those investors that tread on the loose soil of momentum. Fools, however, stand their ground and turn to the words of none other than Ms. Cohen herself for the strength to stay the course:

"Stock selection has again become critically important," Ms. Cohen stated in a 1998 interview. "We like these specific companies (financial stocks) because we like the businesses they're in and their management."

Wow... she sounds... well, quite Foolish!

We've stated time and again that the market won't always be a raging bull. It's so important for investors to build a portfolio based on companies with strong growth prospects and winning fundamentals. Rule Breakers tend to be riskier than your average company, which is why it's essential to stay diversified and keep your portfolio balanced in line with our 13 Steps to Investing Foolishly.

In the Business Week article, Ms. Cohen says, "It's not like I have a crystal ball sending out signals." Ms. Cohen knows it and we Fools know it. Who, then, is putting Ms. Cohen on a pedestal as the Goddess of Markets Future and empowering her with the ability to turn any commentary made for the benefit of the accounts she manages into a self-fulfilling prophecy of massively wide breadth?

Partly it's the media, who reports her commentary as gospel. But it's also partly the fault of investors who desperately want other people to make their decisions for them. If you haven't built a portfolio based on your own research and convictions, your portfolio doesn't have the strength of character to survive the test of shaky days, months, or even years.

Richard Cripps of Legg Mason Wood Walker says of Ms. Cohen's recent moves: "She's sending a signal to a lot of investors that at least someone out there thinks that this isn't going to continue forever."

In case you didn't get the message, this bull market is NOT going to go on forever. No one, however -- absolutely no one -- knows when it's going to end. It may end today, or last for another 10 years.

Invest Foolishly, stay long term, select companies based on research and solid fundamentals, and you can predict that over the long term you will succeed.

That's the gospel according to Fool.