AGNC (and the other similar mortgage REITS) makes its money by throwing ton of leverage at agency mortgages. The agency mortgages themselves are relatively safe since they are guaranteed by uncle sam (though they are still residential mortgages...), but the spread between their safe-but-tiny payments and the rate that they can borrow at to create so much leverage is pretty small. Unlike a commercial office building REIT, AGNC doesn't actually own and/or operate property...they just buy mortgages for the interest payments. Other forms of REITs can be pretty stable and there are real estate investments that don't take the REIT structure (changes the tax implications and means you can invest more in the company where as REITs have to keep diluting their shares with secondary offerings). A well diversified owner of commercial property is going to be no more or less stable than other areas of the stock market...but the yields are going to be more like 5% instead of 20% at AGNC.