Grunching somewhat from the mid first page but I entirely agree with the notion that confidence can be entirely contextual, particularly for those of us with AS, I have no problem with public speaking, I worked as a trader on a currency desk one summer and in the few instances that I had to make snap decisions which had 7 figure implications I felt no anxiety at all, but if you ask me to approach a girl in a noisy bar, ask an friend a question I know he doesn't want to answer or pick up the telephone when I don't recognize the number and I'll go scrambling to find an ativan, I don't understand it but I can relate.
More to the point of your original question though, yeah you can try to fake confidence and hope you eventually get it, but it will almost certainly show until you feel confident in what you're doing, all you can do is try.
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"Doubt is not a pleasant condition, but certainty is absurd." - Voltaire