This topic is a central theme when I practice and teach aikido. Our responses to fear can be grouped into four instinctual responses: fight, flight, freeze, or faint. They have served the species well for survival. They are mostly terrible for the individual. They also show up in smaller scale in less-than-life-threatening conflicts. It is here in the mundane conflicts when instinctual responses create our cultural damage and disfunction.
If predators threaten the group, each individual will have an instinctual response based on their own emotional assessment of the threat and their own ability. These choices are not conscious.
The strong or aggressive may fight, the fast may flee, the stealthy may freeze, others faint.
The strong ones may succeed in killing the predators, even if they are killed in the conflict. Too bad for the individual, but the rest of the group go on to have children.
The predators may be drawn away from the group by those who fled. They may be killed and eaten. Too bad for the individual, but the rest of the group go on to have children.
Perhaps the predators kill the easy targets who froze or fainted. Again, too bad for the individual, but the rest of the group go on to have children.
Practicing a martial art allows the student to learn their own disposition. When faced with an attack from a cunning primate, which instincts show up first?
Does the student fight back? That only works if they're already bigger than their attacker.
Do they shrink from the flight—flee in their body language? That only works if they're faster and able to twist away from the attack.
Do they freeze? That only works if there's cover, or other people fleeing or attacking to draw the attachers attention away.
The essential value of practicing martial arts is learning skills to maintain a felt sense of safety even in conflict so that one's consciousness remains present and not overridden by instinct.
We cannot make constructive choices in conflict unless we can maintain a felt sense of safety.