Personally, I used to have such bad social anxiety/agoraphobia that the others fronted for me until age 24 (am nearing 28 now). I (or jane) spent most of my school years hiding in bathroom stalls at lunch time (unless another was fronting of course). Now I have found a medication (Abilify) that works wonders for that in that I am able to front almost all of the time

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ninchen is cautious/shy/fearful when meeting new people, but opens up pretty fast now. She likes nice people.
Sonja is our 'social part'. Very good at being around/interacting with others. Outgoing, cheerful. Too trusting.
jane is kind of like I used to be with the social anxiety/agoraphobia. She is afraid of contaminating others with her 'badness'. She hides, avoids. SHAME. It look ~3 years before she spoke to our T, with a LOT of coaxing from me.
niva is afraid of attachment. She is aloof around others (though aggressive, usually, to us).
Aiden has schizoid PD. Without empathy. No desire to attach to others. Aloof because he doesn't care/feel (unlike niva who detaches herself out of fear).