It's bad to say....
...but I still haven't got my head around IPv4 yet. With subnet masks etc. I know I should know it by now off the top of my head but I don't. I don't use them enough so always look them up.
But I like going round the house and knowing router is 10.0.0.1. Main PC is 10.0.0.2. 2nd PC is 10.0.0.3 and so on. Can't very well do that with IPv6 can I.
AC due to being embarrassed.