Chris Dillon, a global fixed-income portfolio specialist at T. Rowe Price, said this year could bring the return of the historical link between 10-year Treasury rates and gross domestic product not adjusted for inflation, known as nominal G.D.P. “That’s the alive and open debate for 2015,” he said. “What makes the debate more complicated is the complexities of what’s happening on the global stage.”

Image Heather Loomis of J.P. Morgan Bank, said people are at risk “of throwing in the towel.”

For example, conventional wisdom says that lower oil prices act as a stimulus to consumers, which is good because consumer spending makes up 70 percent of American gross domestic product. But Mr. Dillon noted that companies in the shale drilling and fracking parts of the oil and gas industry borrowed to expand their operations and now, with lower oil prices, they could struggle and hurt gross domestic product. Another weight on the economy could be if the nascent recovery in Europe petered out — or at least provoked anxiety.

“Ultimately, there is much uncertainty,” Mr. Dillon said.

Of course, Treasuries are far from the only type of fixed-income investment. Mr. Dillon pointed to bank loans, municipal bonds and, for at least this year, lower-credit-quality bonds for higher yields.

Mr. Mackay of Morgan Stanley, who says he thinks the Federal Reserve will not raise rates until 2016, is still counseling clients on taking credit, not rate, risk on their bonds. (Credit risk, for example, would be high-yield bonds, while rate risk would be a bet on how the yield curve on Treasuries might shake out this year.)

“You still want bonds, even though yields are going to be lower, as an anchor to your portfolio,” he said. “Inevitably you’ll get some clients who say equities have done well and that’s all I’m going to do. Down the road the equity market is going to collapse.”

Similarly, Ms. Loomis said she had been talking to clients about the need to manage their portfolios with fundamentals in mind, even though certain markets have not been obeying those rules.

“I’d rather say, ‘We didn’t make you an additional 50 basis points,’ as opposed to, ‘We were managing against this trend and it went against us and we lost you 6 percent,'” she said.