In fight or flight, the brain is only able to take in survival-related information, which considerably narrows the field of accessible information. You can again refer to the pages that discuss the information processing and response function of the nervous system and the stages of fight or flight to understand a little more about how this process is impeded during stress. This greatly impacts the ability to take in new information, learn, and understand or do something new.
Prolonged activation of the fight or flight nervous system often plays a role in learning disabilities and social disorders, such as ADD, ADHD, and autism. Carla Hannaford discusses this in more detail in her book Smart Moves, referenced on my recommended reading page.
By strengthening the body’s ability to be in the parasympathetic nervous system state, the brain is naturally able to receive more information to better understand, respond to, and adapt to the world around it.