The result: the worst weekly rout for stocks since the 2008 financial crisis.

The coming week will be another test for investors. Wall Street culture fetishizes forecasts and figures. Analysts and investors are rewarded for their ability to correctly gauge risk, incorporate those assessments into accurate forecasts and then make trades based on them. As a result, investors despise uncertainty, because it makes it difficult to generate good guesses about the future.

And uncertainty is pervasive right now. The coronavirus — highly contagious, with new cases emerging daily, and millions still facing lockdowns in the world’s second-largest economy, China — is creating exactly the kind of unpredictability that makes investors fret. There is little clarity about how long it will take governments and health officials to contain the virus, leading to a gloomy prognosis for global economic growth. Supply chains remain deeply disrupted. Consumer spending may suffer if daily life is disrupted by the virus.

Markets are as precarious as they’ve been since stocks started climbing in March 2009 after the financial crisis. In such cases, investors tend to sell to limit their losses or wait for clarity to emerge, which could take weeks, if not months.

“You need to show that the virus is under control,” said Jack Janasiewicz, a portfolio manager with Natixis Investment Managers. “Until that happens, we’re going to be in these volatile swings.”