[giantrobot]

FB and Twitter don't require subject lines. I think this is one of the biggest factors in their attraction for writing (ignoring social aspects). Facebook and most other social media gives a simple writing prompt "what's up?". There's no need to plan out the post or give it a title. This is the same UX as text messages/messaging over e-mail. You can just write a message.

The implied requirement and/or UI requiring a subject line or title to a post or e-mail is a pain in the ass. People don't want to metacognate on what they're trying to say. They just want to type out a thought or ask a question.

Blog software tends to enforce things like a subject/title because it often generates a URL from it. Facebook et al don't give a shit about such things. A post is just the latest and it gets assigned an ID number.

Even the HN favorite RSS suffers from this because it really wants entries to have titles. They're not technically necessary but most reader software uses titles for UI elements. The implied requirement to title everything I think creates a higher barrier of entry than most people want to deal with.

Even this post I'm typing, if I had to title it I'd probably not bother. I have something to say but having to think up a contextual title for it would be a waste of time and serve no benefit to the point I'm trying to make.