For me it has to be UTXOs I never really dived into it early on, I just saw balances and transactions and thought the way the UI works is how bitcoin works, lol plus I was a shitcoiner so the account model seemed like the default, getting my head around address creation and coin control took some time, I was making a bunch of small transfers and bloating the shit out of my UXTO set

Thankfully i know better now