I am agree about calculations. Moreover, everything should be done precisely. But we are human beings and it mortal for as to fear.
of course fear allowed primitive people to survive in the wild, and fear is present in every person, one is afraid of the dark, the other person is afraid of heights, and fear causes panic,and in a state of panic, people tend to make mistakes
Th fear is also in some way an instinct of self-preservation. So in some cases it is even important.