Nervousness and fear are part of human historic, adaptive, survival biology. It’s kept many life forms alive for thousands of years, helping with escaping or defeating predators.
Fear is a complicated emotional and physiological response to uncertainty, threat and danger. It can be very constructive where it alerts you to potential harm and triggers the chemical reactions our bodies need to respond quickly to ensure safety.
This preparation the mind and body offer as a response to a perceived threat is quite physical, preparing the body for running, fighting or other major physical activity. It is known as the “fight, flight or freeze” reaction where chemicals from the brain and glandular system are released preparing the body to move fast, fight hard or freeze, hoping to be left unnoticed and unharmed.
Nervousness is a survival mechanism that is valuable but rarely needed in contemporary life. It won’t help if you run out of the room or attack the interviewer. For most contemporary challenges you need to pay attention to what you're are thinking and how we are interpreting the situation to not trigger unnecessary fear and nervous discomfort.