The Oracle of Omaha once called this ratio "probably the best single measure of where valuations stand at any given moment."Though the stock market has been a bona fide wealth creator for well over a century, this doesn't mean stocks rise in an orderly fashion. Through the first seven months of 2025, investors have been taken on quite the historic ride.In early April, the iconic S&P 500 (^GSPC -1.60%) shed 10.5% of its value in just two trading sessions, which marked its fifth-steepest two-day percentage de ...