Stocks are in for a rough patch in part because they simply cannot sustain the expectations built into them by investors, argues fund manager John Hussman in a recent note to clients.

“The stock market continues to be strenuously overvalued here, with a variety of historically reliable methods indicating probable total returns for the S&P 500 of only about 3.5 percent over the coming decade,” writes Hussman, president of Hussman Investment Trust.

“This does not necessarily imply much about near-term market returns, though the continuing syndrome of overvalued, overbought, overbullish, rising-yield conditions does contribute to near-term risk.”

NYSE floor traders (Getty Images photo)

Hussman says that unless another asset bubble inflates to replace the previous ones, durable long-term gains will hard to come by in the stock market.

Yet he admits that there will probably be some pretty significant swings in the meantime.

“For example, a series of market fluctuations -40%, +85%, -36% and +100% within a 10-year period would produce a 10-year return about 3.5% annually, so a poor long-term expectation doesn't rule out the likelihood of significant investment opportunities in the interim,” Hussman writes.

“The real difficulty at present is that at already elevated valuations, it's less likely that those opportunities will be front-loaded.”

None of this is scaring off hedge fund manager Barton Biggs. He says buy, buy, buy while equities are cheap.

"I’m still big in U.S. tech, both the old champions and the new contenders," Biggs says in his latest note to investors, according to the Business Insider.

"The former are just too cheap at below S&P valuations in relation to their above-average, albeit reduced-growth prospects."