When someone says they "understand bitcoin" it means grappling with cryptography, mining, ledgers, economics, game theory, fiat currencies, deflation, dapps, etc. etc.
Very few people need to really understand all of that to "get" bitcoin, mainly because most of the use cases aren't figured out. Most people are overthinking at this point and not attacking it from a "how is this useful to me and what do I need to know" perspective, but trying to grok it all, which is pretty hard.