perplexed

Sites like Facebook and twitter are great, because you can get in touch with old friends, post pictures and tell people about your life, and learn things about people you barely speak to. Knowing that it is a public forum, and willingly putting up status updates about your personal life - you are inviting people to comment and weigh in. What I don't get is if people don't want to discuss a private matter in a public forum, why would they post it there?