The stock market's "relative strength index" is the most stretched it's been in 20 years.
And Morgan Stanley says it's the second-most extended since 1928.
According to Business Insider, however, this doesn't necessarily spell impending doom for stocks.
However, it should give investors caution as they consider adding to positions.
The S&P 500 traded above the 80 level that signals the "overbought" condition for most of 2017.
