It takes a single mistake. And in order to get anything done in open source you need to communicate a lot and with many people. So now you're leaving hints about your timezone(s), cultural background, language use. Or maybe you went to that one conference where you talked to five people, one of them describes you to the cops, mentions your accent or the hotel you probably stayed at. Then of course there's the usual DNS leaks, logging in with the pseudonym over the wrong connection. One single mistake.