I think a nice thread starter is to point out a set of facts that are, on the surface, contradictory or counterintuitive. Thus people naturally want to discover the deeper explanation behind the contradiction.

Another thread-starter I've seen in forums is for the OP to challenge an ill-thought-out piece of conventional wisdom. Of course, the challenge must be original, no one wants to rehash trite issues.

Those things said, I don't think I've started any threads on this forum.