I used to post on BBS's and Yahoo Groups with my real name. Then in 2003 during the time I was researching tractors before I bought one, I had a bad experience.
I unexpectedly got buried by 10,000 emails, bounce messages from ISP's all over the world, saying 'recipient unknown here'. The bogus emails that landed on them had my real name as 'Reply To' and random names in the other fields - 'To', 'From', Sent By', whatever all those technical fields are. The content of the emails was Viagra spam, randomized so no two messages were identical. Obviously crafted to evade any spam filter.
Somebody had taken an old program designed to flood Usenet groups with crap and used it to spam their Viagra via email, using real names that I assume they harvested off Usenet posts.
I also got a couple dozen real emails in reply, from calm 'take me off your list' to several burst-a-blood-vessel shrieking outrage ones and a couple of 'did my wife tell you to send this' or 'who told you my secret problem?' The funniest one was from the lady in Office Of Tourism in a Bible Belt state who was outraged when her secretary or somebody gossiped to everyone about what it seemed she had requested.
Ok, it was obvious that the age of innocence on the internet was past. I decided I needed a screen name. One that couldn't be traced through other venues back to me - in the sense that Facebook etc, portrays all the information a stalker would need to go dox someone. So - why not hide in plain sight. A screen name that is unique here but impossible to trace to an individual. I had noticed in the early days here with less than 10k members subscribed and far fewer posting, that nearly everyone at that time was in the Eastern or Southern states. So ... California! Unique here, so my name could be remembered, and at the same time impossible to trace to me alone. I signed up as 'California' after buying my first tractor (Yanmar YM240). And found a community that I enjoy being a part of.