You can blame (or thank) Carl Jung for some of the labels we use for ourselves and personalities. But the thing is, he didn't see the label description as fixed -- he saw it more as fluid. However, after taking the test and reading my description, I don't know that I've changed very much through the years. You may be more familiar with this framework as the Myers Briggs personality test. You can take a self-test here. If you take it, be sure to report back:)
I am INTJ. When I read the description of my personality, and thought about me now and me of years ago, I remembered being 6 years old and my Sunday School teacher telling my mom, "Connie's hard to get to know." I didn't understand what she meant. I remember thinking, "She hasn't asked me anything. If she'd ask me about something, I'd tell her." So as a child, I reacted the way I would probably react now, except now I might worry about what her response to me meant, and think maybe I should try harder to be easier to know.
I think taking a test like this validates who you are in your own sense of self and makes us more accepting of who we are. It's like when my description says "INTJs are perfectionists, with a seemingly endless capacity for improving upon anything that takes their interest" then I relax a little with who I am in that regard, and accept who I am a little bit more. And yes, there are times I really wish I could be one of those other groups of initials -- maybe be more expressive with my feelings, but then I start to analyze it and, well you can figure out the rest.
I find it absolutely fascinating that answering just 72 seemingly random questions can tell you this much about who you are. Carl must have been a genius, coming up with this.