Grantham is worth paying attention to due to his prescient calls over the years. He said that stocks were overvalued in 2000 and again in 2007, anticipating those market downturns
My confidence is rising quite rapidly that this is, in fact, becoming the fourth, real McCoy, bubble of my investment career.
The great bubbles can go on a long time and inflict a lot of pain but at least I think we know now that we’re in one.
MarketWatch 18 June 2020
We found 28 bubbles. Every one of the 28 went back to trend, no exceptions, no new eras, not a single one that we can find in history."
Jeremy Grantham 30/4 2007
"The real McCoy" is an idiom and metaphor used in much of the English-speaking world to mean "the real thing"