Typical MO of a new user:
1. search for a problem online, find posts from SE sites in addition to forums
2. assume SE to be like one of those forums (some users may have prior experience in forms, which may be the opposite of useful, e.g. avoid bumping old threads, moderators establish rules, new users get leniency, and most important, the main focus is less on allowing the same thread to be searchable)
3. they then type up their question, not see a help center, not see the right sidebar explaining what's on-topic until they finish typing and thus think, "they won't mind, right?"