Imagine if Rachel McAdams hadn't auditioned to play Allie? (NEVER!)As hard as it is to imagine Blake Lively not playing Serena van der Woodsen, or Rachel McAdams not taking on the role of Allie Calhoun, Blake and Rachel, just like many stars before them, had to actually audition for their roles. Unbelievable, right?
And it pulls on our heartstrings a little bit to see these characters, now such a big part of our lives, just beginning to form, before taking on the world and being immortalised on the silver screen.
Whether Russell Brand ad-libbing as the hilarious Aldous Snow, or Lindsay Lohan taking on the casting directors at the ripe old age of ten, these expert auditions are what any inspiring actor or actress should look to before attempting to win a role.
Here are some of our favourites...
Emilia Clarke, as Daenerys Targaryen, Game of Thrones
While she says there's no video footage of her GOT audition (yeah, right), Emilia Clarke telling the story of how a sugar high made her do something very... un-Daenerys, is absolutely hilarious.
Rachel McAdams as Allie Calhoun, The Notebook
Guaranteed to make anyone with a heart cry each and every time they watch it, The Notebook is the quintessential romantic tearjerker - and they couldn't have given the role to anyone else after Rachel stole the show with this emotional audition. I mean, you're watching Allie and Noah - those two were made for those parts.
Alyson Hannigan as Michelle Flaherty, American Pie
'This one time, at band camp?' After Alyson uttered these immortal words in the auditions for the teen film - as well as showing she could utter some naughty words without blinking an eye - she was practically guaranteed the role of nerdy Michelle.
Miley Cyrus as Hannah Montana, Hannah Montana
Years before giant foam fingers, X-rated selfies and naked music videos, Miley Cyrus was a little girl who just wanted to be a Disney star.
Selena Gomez as Alex Russo, Wizards of Waverly Place
Who knew this innocent, baby-faced girl who wanted to be just like Britney would end up being one of the most followed stars on social media, a fashion darling on the red carpet and a designer of her very own eco-label?
Steve Carell as Brick Tamland, Anchorman
He had the casting directors in fits of laughter when auditioning for the role of the oh-so-unique Brick, so there was no way Steve wasn't going to clinch the role.
Blake Lively as Serena van der Woodsen, Gossip Girl
A gorgeous Blake downplayed the role of Serena van der Woodsen perfectly in her audition, nailing the character and paving the way to becoming one of the world's most stylish women, both on and off the screen.
Gabourey Sidibe as Precious, Precious
One of the most powerful films in recent years, Gabourey Sidibe played Precious with strength, courage and bravery, right from the very first audition.
Natalie Portman as Mathilda Lando, Leon: The Professional
A baby-faced Natalie Portman nailed her audition as Mathilda Lando - and went on to become of the most in-demand stars of her generation.
Scarlett Johansson as Judy Shephard, Jumanji
It's hard to believe the sought-after Scarlett was ever so young and childlike - but she approached her audition with the maturity and confidence of a much older actress.
Kate Winslet as Rose Dawson, Titanic
A 19-year-old Kate Winslet changed her life forever when she won the role of Rose Dawson, after pulling off an assured, mature audition - with a Jack who wasn't even Leonardo DiCaprio. He was in fact, Elton from Clueless. Yep - pretty weird.
Emma Watson, Daniel Radcliffe and Rupert Grint as Hermione, Harry and Ron, Harry Potter and the Philosopher's Stone
This absolutely adorable audition tape shows three actors just beginning their transitions into three of the world's highest-paid and most recognisable stars.
Lindsay Lohan as Annie James and Hallie Parker, The Parent Trap
Before the mugshots, headlines and community service, Lindsay Lohan was an assured child actress, delivering her lines with aplomb - in both English and American accents.
Russell Brand as Aldous Snow, Forgetting Sarah Marshall
Russell's character in the movie is absolutely hilarious - and you can see why, when even in his audition tape, his ability to improvise and ad-lib is remarkable. He even gets a well-deserved round of applause at the end.
Daisy Ridley as Rey, Star Wars: The Force Awakens
Before being cast in the third biggest film of all time, Daisy was an unknown British actress starring in minor television roles. This powerful audition clinched her the role of Rey shooting her to international fame.
Which one's your favourite? Tweet us @marieclaireuk