'Fight or flight' is the term used to describe our instinctive response to serious danger.

Unfortunately, many people imbue situations with inappropriate import, and they are perpetually in a fight or flight condition.
There are very few situations in everyday life that are literally a matter of life and death.
Letting your animal nature rule you is not a good thing - it puts the body under stress and creates anxiety.

We train to be detached from violence, to remain calm and friendly.
By keeping a cool head and letting our body naturally do the work, we can work more effectively in the face of threat.
The reptile brain may move our bodies into action but it is not allowed to corrupt our temperament with aggression.