None of it is insecurity. We're often more secure than the extroverts.

I don't agree with that hypothesis. I think there are a lot of insecure extroverts, who are looking for validation from whomever they meet. They use others as external judges, assessing their worth through the eyes of others. I have no research to back this up, just my gut feeling.

Actually, I decided to google this, and found one article that does :not perfectly, though) assess the possible insecure-introvert link. This article says that introverts do not necessarily have more mental health problems (e.g, insecurity) than extroverts; rather, extroverts don't like alone time and find it depressing, and they then attribute THEIR feelings to introverts. You can be confident AND introverted, according to this article.

[huffpost.com]

Plenty of extroverts are insecure. I’m thinking of one that is currently living in the White House. There is nothing wrong with being an introvert and we are more comfortable being alone and that can be powerful. I do believe here in America we have a culture that often makes introversion seem to be a weakness, but it is not. It simply means we draw our energy and rejuvenate by being alone. We are also more likely to be independent thinkers, which is why I believe there is a statistically higher percentage of atheists who are introverts

Not at all. Insecurity can manifest in many ways. For instance, an insecurity could make one person shy, and it could make another person tend to overcompensate.

Very little. Insecurities can be remedied.

Many people who are insecure will actually over share with people and over exert themselves to be with others to compensate. Definitely not one and the same

I think you can be wildly insecure, or lack social skills, and still be essentially an extrovert. If you desire higher social stimuli, whether or not you know what to do with it, you are an extrovert. If you find it exhausting, introvert.