The human factor. 

It’s what we must depend on 

when all the glittering technology seems, suddenly, useless.

During a mission countdown, or even a flight test, so many things would be happening so fast that you did not have any time for second thoughts or arguments. 

You wanted the debate behind you. 

So before the mission, you held meetings to decide what to do if anything went wrong.

There was no room in the process for emotion, 

no space for fear or doubt, 

no time to stop and think things over. 

A launch is an existential moment, much like combat. 

With no time to think about anything, 

you had to be prepared to respond to any contingency—and those contingencies had to be as fully anticipated as possible before you pushed the button. 

You also had to be thoroughly knowledgeable about the responsibilities of launch control and range safety.

(Gene Kranz, in Failure is not an Option: Mission Control From Mercury to Apollo 13 and Beyond)