This past Monday marks the twenty-year anniversary of former Fed chairman Alan Greenspan’s famous speech in which he used the phrase in reference to then-stretched equity valuations. In last week’s Wall Street Journal, Steven Russolillo writes, “His call was spectacularly wrong—at first.”

Russolillo offers a Greenspan quote from a WSJ interview: “If you rate me on my irrational exuberance forecast, I get a C. But analytically, it was describing a process that I thought we had to be very concerned about.” The phrase, which has been part of the financial world lexicon ever since, seemed to only boost the market—which rallied for more than three years before the dot-com bubble burst in 2000.

While the ninety-year-old Greenspan “isn’t as worried about stocks today as he was in the mid-1990s,” Russolillo writes, “he is far more concerned about the bond market and the recent sharp rise in interest rates.” According to the former Fed chairman, “The key is not the S&P 500. It’s the 10-year note and 30-year bond that matter. The only thing which is way out of line is the price/earnings ratio in the bond market. And that is not an insignificant factor.”