None-of-your-business attitude
^I understand it's not an overarching trait, but it does seem to be linked when I examine myself. I've thought about what you've said and I've seen the "share too much" thread, but I still can't shake that I don't share things about myself because of this difference in development.
I have some good friends, but I never talk to them about myself. The only thing I talk about is my current interest, which I'm usually obsessing over. Like if I'm obsessing over ASDs, I'll talk to people about myself in relation to ASDs, but I won't bring up what I've done that day or things of that nature. Or I'll talk to them about their problems, and maybe offer some advice (it seems my objective nature is comforting to those who feel afraid or judged with others).
But rarely will I talk about my problems. I don't think anything traumatic happened, I just hide everything by nature and have to consciously choose what to share with others. My parents are very supportive, but I've always wanted to be my own person, without any interference of others. Some people have said this is sad and that I'm missing out, but I find it liberating.
I used to try to form relationships with people through sharing, but it always seemed forced to me. It never brought me anything but stress. Actually, knowing a lot about people sometimes pushes me further away, it's as if they're dumping emotional baggage onto me, which I usually can't handle.
Like I said though, I'm looking at this from my own personal perspective. I have AS, and all three of my boys are on spectrum. All four of us are exactly the opposite. There is virtually nothing my kids won't tell me about what's going on with them, and I was the same as a child. I still am.
Because that's been my experience, I wonder if something else is causing the secretiveness. There were SOME things I kept to myself, but not many really. What I do remember keeping to myself were traumatic experiences. I have one son who did the same thing. He had a very traumatic experience that took him a year to tell us about, but even with that, he couldn't hold it in. He told a friend, who made him come and talk to us about it.
Since that is the light under which I'm reading all this I wonder if something more is going on. I have to wonder if something traumatic happened, or overall childhood experiences may have caused some of you guys to loose faith and trust in those close to you.
I'm not sure I want to ask though, because it's...
well...
none of my business!

Not asking anyone to answer. Just saying compared to what I've actually experienced with AS, this seems really odd (no offense) to me.
EDIT: THIS is what I'm more used to, and tends to be what I see more often posted: http://www.wrongplanet.net/postt184363.html
yeah, I don't get it either. I'm the same as you. I'll pretty much tell anybody about anything. I'm about as open and honest as they come. I don't go around shouting every detail of my life from the rooftops, but i'm not afraid to talk about myself or my experiences. But, at the same time, I walk around fairly silently, not really talking to so many people in the first place.
I too keep things to myself. For many reasons:
- I rarely think about sharing information
- Sharing means talking; I don't like to talk
- I have nothing to gain by sharing
- Anything I share can and will be used against me at some point
- Experience has told me that most people are not trustworthy
I also detest people who ask too many personal questions. Those with such long noses seem oblivious to all the signals I send out that I don't wish to talk about whatever it is they are asking about.
That is what it was like for me too.
The idea to communicate to my parents or other people that I could read in kindergarten or inform them of that I felt sick didn't occur to me. If I was hungry at an odd time I simply went hungry and if I got hurt but didn't cry and didn't bleed then I didn't tell.
It wasn't as if I didn't want to tell but the thought "I need to tell my parents/someone about this" or "I could tell my parents about this" didn't even exist on my mind. I guess they call that a big "red flag" for autism these days in kids.
Even at that one time when I sprained or broke my ankle and had to go to an emergency ward (age 3-4) I didn't ask for help or sought comfort despite that it hurt and despite that I thought that the unfamiliar place and nurses (didn't know that's what they were) were creepy as hell.
Edit: I still struggle with this aspect of communication and social reciprocity.
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Autism + ADHD
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The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it. Terry Pratchett