Or perhaps not. You don't want to retire at a moment when the retirement fund is down 20% and decides to pay no interest on your savings for the next 10 years. Or not pay you at all.
It doesn't really matter. 20% down from peak after 30 years of growth is going to be far over your book value.
Isn't this precisely what target date funds are for?
It doesn't really matter. 20% down from peak after 30 years of growth is going to be far over your book value.