But for a lucky few stars, the people they grew up with became celebrities themselves, with their own fans, their own love interests and their own trending topics.
It must be a welcome surprise. After all, it's lonely at the top, but it's a little less lonely when your childhood friends are there, too.
In honor of International Friendship Day – commonly celebrated on the first Sunday in August – we're rounding up the celeb pairs who have known each other since before they were famous.
Ryan Gosling and Justin Timberlake
Most celebs who knew each other as kids went to school together; Ryan Gosling and Justin Timberlake were co-workers. As cast members on the revamped Mickey Mouse Club, Gosling and Timberlake were self-confessed "partners in crime," hanging out between shoots and even living together for a spell after Gosling's mom moved back to Canada.
"We were crazy," Timberlake told The Jonathan Ross Show in 2013. "We, like, skipped tutoring. Going to the park, to the Honey I Shrunk the Kids set. We'd have milkshakes. Oh man, we were so gangster."
Gwyneth Paltrow and Maya Rudolph
Seth Poppel / Yearbook Library
Decades later, when Bruce's daughter Gwyneth was hosting Saturday Night Live, she used her monologue to give a shout-out to Dick's daughter Maya, who had recently joined the cast.
"This week has been real extra-special to me because one of my best friends is on the show now, and I'm so proud of her," Gwyneth gushed. "She's super-funny and talented, and I'm so glad she's in the cast."
Jonah Hill and Adam Levine
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"Our dads met at the principal's office in junior high," Hill told Howard Stern. "We basically lived together – we were in carpool, sleepovers at each each other's houses, everything."
Hill's first concert was a show featuring Maroon 5 predecessor Kara's Flowers, which nabbed a record deal while Levine was still in high school. Still, the 21 Jump Street star swears that fame has not changed his old friend: "That is a guy who is exactly who he ever was, in a great way."
Besides those kind words, Hill was able to do PEOPLE's Sexiest Man Alive an even better favor, officiating Levine's wedding to model Behati Prinsloo in July.
Leonardo DiCaprio and Tobey Maguire
Martha Noble / Globe
The pair met as child actors in the late '80s, often auditioning for the same roles (which Leo almost always won). Both sons of divorced parents, the two bonded over what DiCaprio later called their "humble beginnings."
As the Aviator star later told the Associated Press, "We both were these young, very enthusiastic, ambitious young men that really wanted to get our foot in the door."
In the '90s, the pair collaborated to make (and then hide) the little-seen film Don's Plum, before forming the center of a pack of young actors with an unprintable name that ran wild around New York City in the post-Titanic era. (Other members of the crew included Entourage's Kevin Connolly, magician David Blaine and Stan from Mad Men.)
"Every project we do, we talk about," DiCaprio told the AP. "Every single choice I've made, I've talked to Tobey about and vice versa. We've had endless conversations about certain projects and argued with one another and supported one another along the way."
In 2013, DiCaprio and Maguire teamed up to play one of literature's most famous best-friend duos: Glittering millionaire Jay Gatsby and his loyal sidekick Nick Carraway in The Great Gatsby.
"I got to work on one of the great American novels with my best friend," Maguire told PEOPLE. "It was great!"
John Krasinski and B.J. Novak
Michael Buckner / Getty
As Novak wrote in his Reddit AMA session, "I sometimes think that if I were to wake up and it turned out The Office was all a dream, the fact that John Krasinski was in it with me would be what I'd realize afterward should have been the obvious tip-off. 'Oh! And John Krasinski was in it, too! But they called him Jim!' "
Nicole Kidman and Naomi Watts
Jeff Vespa / WireImage
The pair later stared together in the 1990 film Flirting, but while Kidman's star rose quickly, Watts toiled along in obscurity. She later credited Kidman with helping her through this tough time: "She kept saying, 'It's just going to take one thing … if you're in a hit film [then] everything changes.'"
The pair reportedly hit a rocky patch in 2013, with dueling biopics and a spat over Kidman's refusal to take part in a celebration of Watts's Oscar nomination. In September, Kidman took over the lead role in Werner Herzog's Queen of the Desert after Watts dropped out, which can be interpreted as a favor, a power move, or nothing at all.
Kate Hudson and Liv Tyler
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The experience was slightly awkward for them. As Tyler told Metro UK in 2008, "We were always so shy about the kissing, but in retrospect we were like, 'We should have just totally made out and tongued each other.' But we never did, we were just too scared to do it."
Jennifer Aniston and Chaz Bono
Splash News Online; Araya Diaz / WireImage
"Every day a group of us would go to Chaz's house after school," Aniston told Allure. "I haven't spoken to him in a while."
Lauryn Hill and Zach Braff
Vallery Jean / WireImage; Millennium / Todd Williamson / AP
"There was a game called Coke and Pepsi: You'd have a partner, and one person was Coke and the other Pepsi," Braff recalled to Jane magazine. "Depending on what the DJ would yell, you had to run and get on that person's lap. And Lauryn was my Coke and Pepsi partner."
Matt Damon and Ben Affleck
"Before Matt, I was by myself," Affleck told Parade. "Acting was a solo activity where I'd just go off and do something, act in a little TV show or something, and no one understood it. … All of a sudden I had this friend Matt, and he gets it and wants to do it and thinks it's interesting and wants to talk about it."
The pair split up once Affleck went away for college – Damon, two years older, had gone to a local school called Harvard – but they reunited in the early '90s in L.A. Both had dropped out of college and were trying to make it as actors. Frustrated by their lack of success, they decided to write their own movie, tossing around ideas for a script about a working-class genius and his townie friends. The rest is history.
Tammie Arroyo / AP; Desiree Navarro / WireImage