I was recently doxxed on Reddit. Never posted my name, used a unique username, but after 6+ years of posting, someone triangulated the data and successfully found my full name and home address.

Even though the user was banned (several times), even though all the posts are now deleted, along with my entire comment and submission history, my username there is now permanently tied to my real name.

While it was easy for a human user to doxx me using my comment history, it's even easier for computers, who save everything, no matter how briefly it is posted, to comb through your data and determine who you are. The only way to stay anonymous is to completely avoid ever talking about anything remotely identifying