If you want a compelling opening act, J.J. Abrams is your guy.

The producer-director has given us some of the most memorable launches and reboots of the 21st century -- Star Trek(2010) and Star Wars: The Fore Awakens(2015) on the big screen, Lost,Aliasand Fringeon the small one.

But one thing Abrams has not done is stick around or return for the more difficult job of closing the series and trilogies he started. Now, with news that he will take over the as-yet-untitled Star Wars Episode IX from fired director Colin Trevorrow, Hollywood's most famous opener will finally be forced to become a good closer.

Abrams likes to talk about a "mystery box" he picked up at a magic store as a kid; he never opened it, preferring the "infinite possibilities" of what it could contain to the actual content. It's telling that he used this as his primary metaphor for storytelling. He likes all the possible ways a story could go more than he likes actually picking one.

Lostis probably the most famous example of the Abrams formula of throwing jaw-dropping elements into a story that someone else will then have to explain. A plane crashes on a mysterious jungle island and the survivors encounter, of all things, a polar bear. Who isn'tgoing to stick around to see how that gets resolved?

The showrunners that Abrams left in charge struggled with finding that resolution for years; the Lostseries finale is now infamous for being unsatisfying and throwing up more questions than it provided answers.

With The Force Awakens, it has now emerged, Abrams was pulling the same mystery box trick. In a New York Timesinterview last week, The Last Jedidirector and writer Rian Johnson basically admitted that Abrams -- his predecessor in the Star Wars sequel trilogy -- had not left him any guidance on the big questions posed by the 2015 movie.

"I had figured there would be a big map on the wall with the whole story laid out, and it was not that at all," Johnson said. "I was basically given the script for [The Force Awakens]; I got to watch dailies of what J. J. was doing. And it was like, where do we go from here?"

That's right: Abrams (along with co-writer Lawrence Kasdan) invented Supreme Leader Snoke, but they didn't have any grand overarching plan for who this shadowy creature was and how he came to rule the First Order and turn Kylo Ren to the Dark Side.

Johnson has already confirmed he's punting on that question, so Abrams will have to resolve it himself in Episode IX -- if he resolves it at all.

The director also didn't have a plan to resolve the other big question of the movie: the parentage of Rey (Daisy Ridley). Johnson says he's resolving that one, but he has also tried to downplay the mystery box aspect by raising the question: does it matter all that much where you came from, or does it matter more where you're going?

Abrams and Kasdan say they were guided by one thing alone: whether what they saw on the screen would "surprise and delight" them as Star Wars fans. Kasdan was out of the Skywalker saga after the first movie too, focusing on the Han Solo spin-off instead. At the time, both expected that Trevorrow would be writing the tricky third act of the sequel trilogy.

The fact that Abrams will now have to do so himself brings a certain sense of karma to the proceedings. It also may bring satisfaction to the Lost, Felicity, Alias andFringeshowrunners, all of whom had to reveal what was inside the mystery box without the original magician's help.

Given that even original trilogy-era George Lucas faced criticism for the way he wrapped things up in Return of the Jedi, this may be Abrams' most difficult challenge yet.

We can at least hazard a guess that there will be no Ewoks this time around -- and certainly no polar bears.