Good scene design helps here. Here's a kind of simple set up:
Context or status quo (the "before")
Big change momen
For example, this is kind of a humorous sketch, not very funny, but it's just an example.
Billy discovered a new species of marmoset!
A year later, it went extinct.
There's the bare-bones of it. (And that is pretty much what I've seen in a couple contest entries this month! Good idea, poor execution.) Have you ever heard a 5-year-old tell a joke? It's like that. Just the punch line.
But the reader doesn't experience in a bare-bones way. The reader probably needs some additional context, some process, some transition. So here's a sketch of how I'd suggest fleshing out that bare-bones treatment:
Set the context: Billy was such a loser! (Maybe an explanation or example here.) He was the sort of kid who read the encyclopedia from A to Z, and would later bore dates by reciting the particulars about different animal species.
Change event: Finally, after failing miserably at school and profession, he found a job surveying the rain forest for resort development. Unfortunately, it was in Madagascar.
Big change moment: One day, while searching for his sextant, which he had dropped in the brush of the forest, he saw a quick little animal, the likes of which he'd never read about in the encyclopedia. He took a photo with his camera, and went back to his tent and emailed the picture to his friend the zoologist. A new species!
Results: Billy became the toast of the zoology world, giving speeches and powerpoint presentations to students and faculties throughout the world. (More here... women zoologists wanted to bed him, men zoologists wanted to shake his hand...)
Punch: Of course, a year later, the species went extinct.
That's just a sketch. But see how by setting up the "loser" context, guiding the reader through the big event and the results, we've given the switcheroo (back) at the end more power.
Our job, at base, is to give the reader an experience, not an outline. Anyone, frankly, can tell the punchline or jot down the turning point event. It takes a -writer- to make it into a joke (or a scene). Execution is all in creating a reader experience, and that goes beyond mere plotting of events into presenting not just the events but the context and process and consequences... and in the most effective prose too.
No, it's not easy. But deciding to do it well is the first step to doing it well!