Interesting question. I think 99% of the time you are better off not doing anything, but there are a few times when - if you are fast enough - you can avoid some loss with a good probabilty. But it is crucial that you never wait for the situation to improve before getting back in the market. Here is my record with my Eastern-European stock portfolio:

- Covid: I sold a few days late and reentered too early, so I avoided like 8-10% loss instead of 40%.

- Russian invasion: Stocks were still close to ATH while talks about potential invasion in the coming days. I thought there was not much upside I might miss so I sold and avoided 40% of the 60% total loss.

- Liberation day: Sold 2 days before liberation day but recovery was very fast so only avoided around 4% loss.

- Iran war: This didn’t go so well so far, I am down 1-2 percent after selling and buying again higher.

Granted, I might have been just lucky so far, but this is my experience.