Hindsight is a not terribly useful during a crisis.
It diverts attention from the immediate priorities. It fosters blame. It retards action (because we cannot go back to the past to fix things); all these is more fuel for the fire at hand.
Image from Know Your Meme
Instead of "what is the crisis here and now, and what can we do not to minimise damage", hindsight distracts us with "how could this happen, why is this happening, and whose fault is it?"
Hindsight is very useful, however, in the post-crisis reflection and learning phase. When we can calmly analyse what happened, why it happened, and how we can do better next time; without becoming emotionally overwrought.
Are you in the midst of a crisis right now? Don't call Captain Hindsight!
Are you reviewing the year? Don't beat yourself up over what you could've should've done.