Other than that, I'm pretty open to people when it comes to other aspects in life. If they ask me about myself and they are someone i know on some level, then I'll answer gladly. I only avoid talking about myself, when I feel like i am not going to be coherent ,because it has caused misunderstandings before.
I don't usually hide alot from my friends or my family. And if I do, it's because I, myself, am not sure of what I want or how I feel. So, I retreat back into my introversion and figure things out, and once I do, I'm ready to interact and talk or answer questions. Or, I hide what drives me in life, things that keep me motivated, like a beleif or wish or purpose, then yes I would want to protect it from passer-bys and strangers, because it's what keeps me going.
I think the main reason behind my introversion is that I just really like to be inside my head, generating ideas, examining possibilities, and predicting and playing out scenarios.