Even big-shot Hollywood studios sometimes have to settle for second best. Sometimes it's because the actor they really want is committed elsewhere, other times it's due to changes in production staff or down to the whims of the studio heads who hold all the cash.
Often, these potential castings aren't even aware that they're under consideration, whilst others end up cursing the stratospheric success of those that get the gig. Hell, some poor actors still are recast during the production itself.
These What If? scenarios provide tantalising glimpses of an alternate reality. A parallel universe where, for example, Ferris Bueller AKA Matthew Broderick played Heisenberg AKA Walter White (there's a blue meth/Bueller pun in there somewhere). Likewise, wouldn't you want to live in a world where Robert De Niro's 'Big' plays regularly on ITV2?
It's a fun game to play with friends, wondering which actors could differently inhabit a well-known role. This list plucks just some of the many enticing casting possibilities from film history and imagines how things may have turned out differently.
10. Margot Robbie as Sue Storm (Fantastic Four 2015)
Margot Robbie is one of the undisputed jewels in the crown of the DC cinematic universe. She livened up the grey and dismal Suicide Squad and has been an absolute joy in Birds of Prey and The Suicide Squad. Long may she reign.
However, things might have been very different had she been cast in Josh Trank's flop of a Fantastic Four film back in 2015. Robbie auditioned for the role of Sue Storm and eventually lost out to Kate Mara. Given how much of a force of nature director Josh Trank was reported to be (allegedly getting into heated physical confrontations with people on set, including star Miles Teller) Robbie's presence would likely not have made much difference to the finished product.
Allegedly butchered by studio interference, the film was a critical and commercial disaster - and no one's crying out for the Trank Cut. Which isn't to say that Margot Robbie can't still give good work in disasters - just look at Suicide Squad.
However, of the Fantastic 4 cast, only Michael B. Jordan appears to have gone on to bigger and better things in both the Creed films and Black Panther. Luckily for Robbie, Harley Quinn was just around the corner.