Adobe Stock/Andrey Popov

The U.S. 10-year Treasury yield inched just shy of 3% Monday morning, which is a level investors say is worrying, CNBC staffer Silvia Amaro reports.

The 10-year Treasury yield was at 2.9882% at about 6:20 a.m. ET. It hasn’t hit 3% since 2014.

Here’s how we got here:

Subsequently, yields have mostly followed a downward path on the back of support from central banks, which tapped into bond markets in the wake of the global financial crisis in 2008 to boost their economies. But their prolonged intervention has made investors accustomed to their support and to the guarantee that central banks would be there in case things turned badly — leading to higher equity investing, when investors buy shares of companies.

As the 10-year yield stops following that downward trend, it raises concerns that the positive outlook for equity investment is about to end.

The 10-year yield is used as a benchmark for many financial instruments, including mortgages and as a barometer of investor confidence. Amaro writes that the 3% level has a "psychological" aspect that makes markets anxious.

Pro says there are three reasons 10-year is rising from CNBC.

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