Brian Krebs (krebsonsecurity.com) has a lot of fascinating stories on his blog on doxxing and revealing identities of people for whom remaining anonymous was vital (spoiler alert: they couldn't).

Keeping totally separate identities across different services is key (using unrelated usernames, avatars, emails for every service). It’s also extremely difficult and unpractical to pull off.

In most doxxing cases perpetrators manage to get access to a single service and use it as a foothold to penetrate to other services. For example, someone learns your email from a forum, somehow hacks your email, gains access to Dropbox and finds the scan of your passport, driver's licence and social security card. Email in general is the key one's digital kingdom so the surest way to minimize the blast radius is to keep everything separate and unrelated.

Edit: typos