NEW YORK -- Ignoring warnings from Wall Street skeptics is as American as apple pie -- especially when stock prices are rising and investors are making lots of money, as they have since the market took off in early March.

Sometimes, shutting out bearish lines of thought is a profitable strategy. But it can also prove to be dangerous to an investor's financial well-being if the advice to proceed with caution turns out to be correct.

Economist David Rosenberg knows firsthand what it's like to alert clients to potential trouble in the world of finance only to be dismissed by disbelieving and profit-hungry bulls. So does fellow economist Nouriel Roubini, who as far back as the spring and summer of 2006 went public with his view that the U.S. was "vulnerable to financial shocks" and heading for recession.

Both men are again warning of potential trouble. And just like a few years ago bulls are paying little attention.

In the years leading up to the recent financial crisis, no matter how many times Rosenberg, then at Merrill Lynch, raised red flags about the bubble-licious housing market, or gave clients a heads-up about what he insisted was a financial disaster in the making, no one seemed to listen.

"Back in 2005 and 2006, if I looked clients in the face and told them housing was a bubble, it was like telling them their kid was ugly," recalls Rosenberg, now chief economist and strategist at Gluskin Sheff.

Indeed, despite his objective, data-driven and historical approach to market forecasting, Rosenberg's straight talk about what could go wrong was viewed as borderline radical, akin to an investment idea wrapped in a tie-dyed shirt rather than a blue pinstripe suit.

Says Rosenberg, "I recall that people like myself were viewed as borderline lunatics before the financial crisis broke."

It turns out the lunatics were the people who stayed fully invested and lost a bundle of money when financial markets collapsed.

Fast-forward to October 2009.

A handful of respected market sages who got it right in predicting the worst financial and economic downdraft since the Great Depression -- guys like Rosenberg and Roubini, chairman of independent advisory firm Roubini Global Economics and an economics professor at New York University -- are again warning of potential potholes ahead.

Their message is again having trouble going mainstream. Bulls are again skeptical of these high-profile forecasters -- even though the financial future they foresee is once again filled with storm clouds.

Wednesday, the S&P 500-stock index sank 2% to 1042.63, extending its recent pullback to 5%. The broad market gauge is still up 54% since the March 9 low.

Roubini warns that the big run-up in stock prices since March is being driven by a "wall of liquidity" and "momentum trading" and classic Wall Street "herding behavior." Part of the rally, he says, is justified by economic fundamentals, which have improved because of the government's backstopping of the financial system. Stocks have also rebounded because the odds of a depression have fallen significantly, taking the so-called Armageddon trade off the table, he adds.