In March 2009, Wall Street was a fearful and anxious place, where fortunes had been decimated and retirement funds deflated.

What few people could foresee in the depths of the Great Recession was that the stock market was also on the verge of a historic recovery, one that persists today. The decadelong run is also raising caution flags for some analysts who worry that investors are accepting too much risk.

Stocks are finishing 2019 on a remarkable upswing, with all of the major indexes hitting record highs and the S&P 500 up nearly 30% for the year.