The European markets have been exuberant for months. Propelled by an improving economic climate, investors have been eager to make bold bets on risky assets like Portuguese bonds, Spanish construction companies and Greek banks.

But investors received a jolt on Thursday when shares of Portugal’s second-largest bank, Banco Espírito Santo, were suspended from trading, prompting fears that the bank might need to be rescued. The move sent high-flying stocks and bonds in Portugal plummeting, forced two Spanish companies to suspend bond offerings and brought concerns over the health of Europe’s banking system.

As markets from Germany to Greece wobbled, the tumult was a reminder to investors as to how quickly bad news can spread in the euro zone. At a time when the European Central Bank is scrutinizing banks, the problems at Espírito Santo are raising fears that there may be unpleasant surprises in banking systems in Greece, Spain and Italy.

In short, investors had to own up to the economic reality that Europe — while on the mend — is still in a precarious place.