Investment bankers don't get paid to be pessimists. Throughout the current slump in takeovers, mergers and acquisitions (M&A) advisers have said a recovery was around the corner, awaiting a stronger U.S. economy, rising stock markets, or an end to the European debt crisis.

All three of those conditions have now been satisfied, yet deal-making has remained stagnant as CEOs continue to worry about the viability of the economic recovery. The final three months of 2013 saw announced takeovers slide by almost a third from a year earlier, even as the outlook improved in Europe and North America, according to data compiled by Bloomberg.

The sustained slump has flummoxed M&A bankers, whose employment depends on the prospect of deals. It may portend a shift to lower takeover volumes, which are now at their lowest ebb as a proportion of stock-market capitalization since the 1990s, Deutsche Bank AG data show. The best bet for a deals recovery in 2014, some bankers say, is a run of economic growth that's not propped up by U.S. Federal Reserve bond-buying, which the central bank this week began to curtail.