In my case, I was so embarrassed by some of the really STUPID things my dad would say when (very seldom) he was in a social situation. So my thing was to speak so softly that no one could hear me because if I said something WRONG I was afraid of sounding as STUPID as my dad.
I could give speeches on topics I knew well but just answering questions or talking with people I went into quiet mode. I finally broke out of that at 54 when I finally got out of the bad environment I had been in....though my dad had died at least 15 years before that. When I got out of the bad marriage, I could think clearer & retain things I read & that opened up my ability to truly become part of discussions. Go figure, that was after my computer design engineer career was over. I sometimes look back & wonder......feels like I an thankfully NOT the same person I was.