152 years of S&P500 returns

 From Visual Capitalist

Observe how the returns are skewed to the right, i.e., are greater than zero.   And how big falls are not always immediately followed by big rallies--for example, 1931's -50% was followed in 1932 with -10%.  1933, however, was between plus 40 and plus 50%.   There were a couple of bear traps (false rallies) between 1929 and 1933.  And the level of the S&P500 didn't pass the 1929 peak until 1954.

US share market at record concentration

 From IsabelNet

The US share market is more concentrated than it's ever been.  And that makes it risky, because most of the top ten stocks are from a single industry: AI/tech.  

AI is proving very costly, and is not yet generating anywhere near its cost in revenue.  The last time this kind of euphoria overtook markets was during the dot com boom at the turn of the century.  And that ended badly, with the S&P500 falling 50% over the next two years.  Some of the hot favourites (Amazon, for example) eventually went on to become billion-dollar companies; most vanished without trace.

Bubbles almost always pop.  They rarely deflate softly.