Some Historical Perspective

 One chart… SP500 in log scale, annotated with four seminal tops and crashes in the last 40 years.

The current run is by far the longest and has an unprecedented climactic extension, as trillion$$ have been pouring in - an unintended (?) effect of pandemic cash.

The recovery from the debt crisis took huge, coordinated cash injections from most all central banks, which continued for years and fueled markets with negative real interest rates.  Until the pandemic hit and central banks made the previous cash torrent look like a drip.  Predictably, but definitely not necessarily, markets have gone - literally - ballistic.

Valuations of everything, from lumber to junk bonds, have become manic.  It remains to be seen how central banks react to the next crash… print even more?