Fortunately, YOU author this story. Unfortunately, you get one sentence. Fortunately...

Fortunately, you get to author this story.
Unfortunately, your contribution is limited to one sentence.
Fortunately, it is as simple as adding a single (Fortunately/Unfortunately) sentence, via a comment below.

Unfortunately...this story has seemingly reached its end.
Fortunately, this is untrue - the parameters have been laid, and the true story now begins...

Fine print

• Feel free to contribute repeatedly; just never twice in succession.
• Please use common sense; avoid any commonly-bannable topics.
• Upvote and Follow me if your future brain might dig what my future brain thinks.
• Have fun!