Please guys...read and study more... past declines, past market behavior, past market psychology. 2008 had real, hardcore financial problems that affected a huge US industry. USA came close to going bankrupt. Today we have none of that (we actually have some amazing new technologies that will shape the world long into the future). However, the Fed came in and induced massive levels of stimulus, and these stimulus ended up going much longer than they should have and even increasing (as per each new Presidential wishes). They should have come off long before covid. All of this stimulus has to come off. These new technologies need to grow and thrive on their own.
Looking at the charts, even the likes of Microsoft and Intel had large crashes in share price between the 2000 peak and 2002.
It's not really the fundamentals or financials or the numbers/statistics, it's the investor/trader's reaction to them over time. Different fundamentals, financials, numbers, statistics, etc. can cause the 'same' reaction in traders as they had in, say ... 2008, (or any other year). If traders feel the same way they did in a past timeframe, and in the same proportion, history can repeat. (Exception being when comparing a non-trading curbs timeframe with a trading curbs timeframe, when the curbs were actually used.) This is why bubbles can form and last despite there being excessive valuations. The numbers don't cause bubbles, the people do, regardless the numbers.