waltworks - Which would you trust more: my opinion or historical data? I assume you'd say "historical data", yet when you promote index investing you tend to provide your opinion. Why not point people to historical data, to convince them indexing is better? (Like SPIVA, which compares the S&P 500 against active funds). That's definitely the approach used in the book "A Random Walk Down Wall Street".
Buffaloski Boris, bthewalls - Most market timing that I've heard about attempts to sell before a crisis, avoiding the damage, and then buy back near the bottom. Although I timed the March bottom one day early, I'd grant the bottom is normally hard to time.
What about making the first timing decision during a crisis? Meaning you don't sell before the crisis, but just wait for a deep enough crisis, and then make a timing decision. I'm putting forth the idea that you switch 1/5th of your portfolio into the most beaten up individual stocks. During the 2008 crisis, that would be banks, REITS and home builders. During 2020, that would be retail, airlines, restaurants.
That makes the second timing decision much easier: wait for a recovery. You bought the stocks after a significant drop, and you wait for a recovery. Worth noting about drops & recoveries:
20% drop (4/5) needs a +25% recovery (5/4) ... 4/5 x 5/4 = 1
33% drop (2/3) needs a +50% recovery (3/2) ... 2/3 x 3/2 = 1
If index funds drop 20%, and you bought individual stocks that dropped 33%, you get a recovery that's twice as strong (+50% versus +25%).
It's still two market timing events, but "waiting for reversion to the mean" is easier and more likely than timing the bottom of a crisis. So maybe that's an improved way to market time... I'll let you know in a year or so. :)