One – hold their stocks and bonds and ride down with any market declines as the markets always come back. (Many sell at the bottom).
1a, 2a - people who earn enough more than they spend build cash and buy the dips.
Then engage either one or two.
You know investors that have dividend paying stocks that they bought at much lower prices are really really reluctant to sell them. Their rate of return has grown as dividends were raised over the years. Retired people especially will not want to sell this income producing source.
Most people with 401k plans and IRAs likewise are reluctant to ever sell.
Pain threshold. Selling happens to long term investors when they just can't stand the pain any longer. (This is often at the bottom).
It used to be that in the end, you either have faith in American enterprise or you don't. Now, the world economy is financialized and asset classes are correlated.
But it still comes down to the same decision. Do you have faith or don't you.