If you're someone who is highly prone to stultifying bouts of nervousness, don't beat yourself up. First, doing so could make your anxiety worse. Second, you have a much more available scapegoat in human biology and evolution.
To put it very simply, nervousness and fight-or-flight reactions are physiological reactions to stimuli that our body wants us to watch out for. In the past, those dangers were sometimes mortal ones — dangerous terrain, flora, and fauna. Today, as ASAPScience explains, we experience the same "threat level" from things like first dates, competitions, and job interviews.