I had a friend seeking assurance from me in 2008 that remaining invested was the right move. I told him that his brave behavior prevented crowding of the exits while people like myself were selling.
When it a banking collapse or a pandemic I've found it wise to sell everything early. Once the searing pain has stopped I get greedy looking for new entry points - it works for me.
What I ignore are garden variety declines lie we're currently experiencing.
The trick is determining which is which. In 2008 I sold everything before the market declined, with the pandemic the market decline was needed to wake me up.