What if Indiana Jones had been played by Tom Selleck? (He almost did.) How about Courtney Love in "Moulin Rouge"? (She tried out.) What if Forrest Gump had been played by Gary Busey? (OK, so we made that one up.)
But, it's easy to forget that in the world of filmmaking, competition takes place and nothing is in stone. It's real life.
Take casting. Roles usually aren't "written for" anyone. Thus, all those big names have to come out of the woodwork and make their pitch. And at the end of the day, the role goes to victor. But what if the victor had been another?
Jack from "Titanic" didn't have to go to Leo and the role of Rambo didn't have to go to Sly. And can you imagine anybody but Michael J. Fox playing Marty McFly in "Back to Future"? Stop imagining because the role originally went to Eric Stoltz.
Who tried out for which roles? And how different would things if Leo and Sly didn't win? Today, we look at five "what-ifs," starting with arguably the best sitcom ever ...
No. 5: Rosie O'Donnell as Elaine on "Seinfeld"
Back in the day, Rosie O'Donnell had been a aggressive yet good-natured performer who entertained audiences with her stand-up and on the screen. So it made sense when her agent called with a sitcom audition for a strong and funny female lead.
The character's name was "Elaine" for a new sitcom then known as "The Seinfeld Chronicles." This role seemed all the more appropriate as Rosie was quite familiar with Seinfeld's material. But, of course, the nod went to Julia Louis-Dreyfus who may be known as "Elaine" for all eternity.
But had O'Donnell gotten the role, how different the show would have seemed! This is especially true given Rosie's subsequent success and controversy as a TV personality. Looking back, this rejection was a significant determiner for a historic sitcom and a successful daytime career.
But our next case of alternate casting involves a much more established star missing out ...
No. 4: Johnny Depp as Jack in "Titanic"
Even harder to imagine are the biggest of the stars being rejected. But it happens.
Johnny Depp had to sit back and watch "Titanic" unfold to its box office glory with another actor at the helm: Leonardo DiCaprio. And you know darn well it must have been frustrating for Depp seeing all that success knowing he was turned down for the part. "It should have been me!"
But like any motivated and determined person, Depp just had to suck it up, realize that's how the business works, and say "on to the next one." This, of course, he has done multiple times over.
And while we're talking Depp, another of his misses is significant. Had he gotten the lead in "Mr. and Mrs. Smith," who knows if "Brangelina" would have happened. Who would the tabloids be writing about then?!
Our next snubbed actor was also upstaged by Leo ...
No. 3: Jim Carrey as Howard Hughes in "The Aviator"
Again, you'd think the power indicated from Jim Carrey's $20 million price tag would make him practically immune to competition. But he's not the only A-lister out there.