Introvert and Extrovert

There is an idea of deciding people's character for introvert or extrovert by Curl Young.

I do not know the reason why people are separated into these categories.
It is said these are related to DNA, and our relationships with childhood, and our habits, and the degrees of narcissism of the people, I am no idea about that, or habits or all of them, which forms unique chiropractor of a person. I do not know the reason. I need to read books on these topics in order to have deeper understanding.

Anyway, I do not know why, and I really like to connect to others and be with them, but

I prefer focusing on my ideas or reading books on several subjects  and sometimes I want to escape from others in nature and be alone, working on my own ideas about something or planning.

I do not know why and it is not good or bad.