The 2007 - 2009
bear market decline wiped out not only the bull market advance that followed the 2002 low, but the entire total return of the S&P 500, in excess of Treasury bills, all the way back to June 1995.
This instance may be different in the near term, but a century of evidence argues that the completion of the
market cycle will
wipe out the majority of the gains observed in the advancing portion to - date (even without valuations similar to the present, the average, run - of - the - mill
bear market decline has erased more than half of the
market gains from the preceding bull
market advance).