How would you know what you would do, until you actually had to do it?

With recent catastrophes, fishing boats capsizing in Gulf of California, hurricane Irene, revisiting 9/11, etc, a lot of armchair QBing goes on. People say if they were there, or it happened to them, they would have done this or that. That made me think, it is easy here safe at home in hind sight to know what path to have taken, but in the throes of the commotion and chaos, would I? I know if I were in the towers I would have left the second tower just in case the other tower fell over. I would have been thinking the worse even if I wasn’t thinking it happened deliberately.

The fishing boat going down in the Gulf of California I don’t know if I would have made the right choice, remembered to go in the right direction, etc. If I get woke from a dead sleep knowing that I will be in the water and I am not a strong swimmer, and with everyone else scrabbling about I am not sure how rational or calm my thinking would be.

How can anyone know for certain what they would do, and how they would do it, until they actually had to do it?