This is the Fed's biggest economic headache

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Fed's Fischer: Rate hike high probability in 2015

If investors learned anything from Fed Chair Janet Yellen's testimony to Congress this week, it's that the central bank is willing to wait for inflation to catch up to employment before hiking rates.

It could be a long wait—longer, in fact, than many market participants anticipate.

Language tweaks in Yellen's semiannual appearance Tuesday and Wednesday sent strong indications that even if the Fed removes the word "patient" from its next post-meeting communique, it will remain, indeed, patient when it comes to rate hikes.

"The more I think about it, the more I feel that Yellen was very dovish," David Rosenberg, economist and strategist at Gluskin Sheff, wrote of the testimony. "If a shift in policy was coming, this was the setting for verbalizing it—she passed up the opportunity."