I believe that all of us are born extroverted by nature. Think about how babies typically need attention constantly, its human nature biologically speaking.. As we grow, we are heavily influenced by everything around us, which plays a role in how we can become more introverted. Some children get more attention from siblings or adults, may cause them to become more extroverted. Those who get less attention become more introverted. Introversion can also cause more mental sadness/instability in life. Take a look at the serial killers and mass shooters personalities, often they were neglected and kept to themselves. However the mind is bendable, this can be changed if someone will work for it. You ever notice you become happier the more you interact with others? Extrovert behavior would be most beneficial in terms of mental and physical health, hence thats why many who are not want to become. The article makes sense.