Are High Stock Prices Sustainable?

Why I Cashed Out of the Covid-19 Rally

https://www.bloomberg.com/opinion/articles/2020-05-12/why-i-cashed-out-of-the-covid-19-market-rally

Clive Crook:

“An investment strategy of “Don’t just do something, sit there” has served me well over the years. So it was with some trepidation that I set it aside: As of Friday, alarmed by the recent surge of stock prices, I’m all cash.” 

Update:
Wall Street Heavyweights Are Sounding Alarm About Stock Prices
https://www.bloomberg.com/news/articles/2020-05-13/wall-street-heavyweights-are-sounding-alarm-about-stock-prices