When you were younger, maybe you and your sister got into petty fights. Maybe she stole your favorite t-shirt, then immediately spilled chocolate ice cream all over it. Maybe she told your mom about your secret crush after you explicitly told her not to. But for all the times she’s pushed your buttons, all close siblings know that nothing compares to having a sister as your bestie.

It’s tough to compete with someone who’s been there for you for your entire life. Your sister is the person who comforted you when your heart was the most broken. She’s the first person you called when you found out you got your dream job. Your sister knows everything there is to know about you, and you know everything there is to know about her. You’ve been through thick and thin together — and you know you can always count on her to have your back.

Tina Fey and Amy Poehler reunite for Sisters, a new film from Pitch Perfect director Jason Moore about two disconnected sisters summoned home to clean out their childhood bedroom before their parents sell the family house. The movie is definitive proof that siblings make the most epic of BFFs, and we couldn’t be more excited to see the film when it hits theatres December 18, 2015. But just in case you need more proof of sibling bestie-hood, here are just a few more reasons why it’s all kinds of amazing to have a sister as your BFF.

You never run out of things to talk about

When you’ve known someone for your entire life — and lived with them for a good portion of it — chances are, you have a lot to talk about. Your conversations are never-ending, and you couldn’t imagine it any other way.

There’s no need to impress, because she’s definitely seen you at your worst

Let’s be real: Once someone has seen you poop your pants as a baby, the jig is up. From the morning after your first high school party to that time you finger painted the walls with peanut butter, your sister has seen it all. You can wear your oldest, ugliest sweatpants around her while eating chips off your stomach, and she still wouldn’t care.

You trust her advice over anyone else’s

Even if you don’t like what you hear, you know your sister has your best interests at heart. She knows you better than anyone, so it’s no surprise she’s the first person you turn to when you’re in need of some sage counsel.

She probably knows (or knows of) every person you’ve ever met in your entire life

This includes obscure family friends, weird childhood neighbours, distant relatives, and your embarrassing crush from the 4th grade.

Borrowing things isn’t a big deal

You probably do it without asking most of the time, and you know she does the exact same. You borrow things so often, in fact, that sometimes it’s even hard to tell whose closet you’re looking through.

No one understands your parents like she does

A sibling is the only other person who gets to see what your family is really like behind closed doors. She’s the first person you turn to when you need to air your parental woes, and you can always depend on her for a mutual eye-roll about a dad joke.

You have a lifetime of inside jokes together

To an outsider, some of them might sound absolutely ridiculous — if not completely nonsensical — but you both know what to say to get the other rolling on the floor in a fit of giggles.

You can always call her for a bail out and not be embarrassed about it

When you can’t call your parents to get you out of a sticky situation, your sister is your #1. There’s never any judgment (and if there is, bailing you out comes first), and you can always trust her to drop everything to come save you.

Even if you fight sometimes, you still love each other unconditionally

All siblings fight. When you’re with someone basically 24/7 through childhood and adolescence, it’s inevitable that you’re going to get on each other’s nerves. But you always know that the feelings are temporary; and even if you don’t like your sister very much when you’re fighting, you still love one another more than anything.

You always have someone to reminisce with

If you ever start a sentence with, “Remember that time. . .”, her answer will always be, “Yes.” Whether good or bad, your sister is there to talk it through.

You can share a bed/toothbrush/basically anything else, and it’s not awkward

Her germs are your germs. Chances are, you’ve shared these things on multiple occasions throughout your life — so there’s never anything weird about doing it in adulthood.

You get to watch each other grow up

There are few things as incredibly gratifying as getting to grow up with your best friend. You get to see one another go from sloppy kids to functioning adults; and the fact that your bestie is also your sister makes this all the sweeter.

You know that nothing can ever come between you

Everyone knows the phrase, “Blood is thicker than water.” Friends come and go, but your sister is forever.

Sisters hits theatres December 18, 2015.

(Images via Sisters.)