The problem is the way we are told to treat adults as kids.
We go all the way through school repeatedly being told that the adults have the answers, they understand everything that we don’t, they know how to tackle the things that seem to big for us, and, most importantly, they don’t make mistakes.
So now that we’re adults, even though we cognitively know by now that it was all bullshit, it’s hard to turn that training around. We make mistakes, don’t have the answers, and sometimes struggle with parts of the world that we’d expected would make sense by now. We know that the adults before us were no different, but it’s been so long that it’s hard to internalize that we, now, are just like them.
Your imposter syndrome is programmed. It’s not your fault.