Others on this thread have spoken to their impostor syndrome. I won’t answer with that: we are all, as Michael Masiello once put it to me, broken toys here, which correlates with us falling into our knowledge rather than training for it.
I’ve never formally studied Ancient Greek, for example.
I don’t say anything online I’d be ashamed of (including for this question); but then again, I tend to be an open book, both in person and online. In person perhaps less than I used to be.
People on Quora have been surprised about stuff I know that I don’t post about much. My day job being in education technology (h/t Scott Welch), for example, or that I program a fair bit, though not necessarily well (h/t Miguel Paraz).
People have also been surprised about my age. As of yesterday: 45. I certainly don’t act it, and I don’t plan to.