Why calm down the nervous system first:

When a person feels like they are in a state of fight, flight, or freeze all the time, “the old reptilian brain” kicks in leading to a rapid heart rate, sweaty palms, difficulty swallowing, and tight muscles. It shuts down the “new brain,” or the part that is used for critical thinking. Very little information is able to be absorbed. If everything around you feels like a threat, it is hard to relax.

Until a person can teach their body how to turn off the fight, flight, or freeze states it will continue to react to the world around it.