heres a chart that’s adjusted for inflation
It peaked at 5500 in 29
It didn’t go significantly above that and stay above that until 1995 ish
That’s 60 years of almost zero gains
I believe you said "several" spans. You've referenced one span and I don't know how you couldn't argue that was an anomaly. Further the fear implicit in your comment is that one invested all of their money in August 1929 and not a penny before and not a penny after. I would be curious to see what the ROI chart would look like assuming someone invested an equal amount per day (or per month) over that period.
I'm not saying a severe market crash can't happen again but I won't let what happened in 1929 keep me from investing 90 years later. I believe sticking to the fundamental recommended approach of dollar cost averaging hedges against the risk of getting whipsawed by downturns (even severe ones). I survived 2003 and 2009 and came out much better in the long run because I was willing to invest when other folks were panicking.
All of this being said I unfortunately think the market does need a breather and don't doubt we'll see some profit taking at some point. I've got some money on the sidelines and I think I'm going to split the baby and put part towards the mortgage and keep some in the back pocket just in case a buying opportunity arises. Yes I realize I'm trying to time the market which is a no-no but that is a risk I'm willing to take.