The balance of jobs and workers can quickly change as more people enter markets with little-to-no unemployment. That's why Boehner cautions young people not to choose a career track in an advanced specialty simply because it's currently in demand.

"If you're going to school for 11 years, what's hot now may not be hot in 11 years," she said.

The U.S. job market currently has 8.1% unemployment. While almost everyone agrees that's too high, zero unemployment wouldn't be a good thing either.

An economy with no unemployment is like a stagnant real estate market, said University of Oregon professor Mark Thoma.

"Suppose every apartment in the country is full, and I wanted to move from New York to Los Angeles," he said. "I would have to find someone in L.A. who wants to move to New York, and we would have to do a trade. It's much more efficient to have some vacancies."

Some churn in the labor market is a sign of a healthy economy, said Chris Pissarides, a Nobel Prize winning economist at the London School of Economics. He estimates that even in the best of times, regular turnover in the job market leads to an unemployment rate around 5%.

Add on structural changes that can put people out of work -- for example construction workers after the housing bust -- and full employment is probably somewhere around an unemployment rate of 6%.

"In an economy that is really growing fast, there's always a need to reallocate workers either across the country, skill categories or industries. People may need to change jobs," Pissarides said.

"Therefore we have to accept there will always be some unemployment and it's good for the economy."

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