Sisters are bound together by family and are stuck with each other for life. It's not a given that your sister will turn out to be your best friend, but when it does happen, consider yourself very lucky.
The sister best friendship is a magical relationship. But, it's different than friendship. The two of you have been intricately intertwined throughout your lives (or, if you're the older sister, most of your life).
She was there before you asked her to be. You didn't seek each other out; the universe gifted her to you.
It's for these very reasons that sisters aren't always best friends. Sometimes, they're not friends at all. Sometimes, their closeness drifts in or out with age.
But, if you've been blessed with the sister best friendship, these are 16 unique, irreplaceable elements of your lifelong sister love affair:
1. You feel so much pride for her.
You're constantly in awe of her. You are her number-one fan and support everything she does like crazy.
You are so proud that she's your sister that you want to scream it from the rooftops.
Whether she got a job promotion, found a $20 dollar bill on the sidewalk or finally popped a stubborn pimple, you think it's the greatest thing on the planet.
2. You're not going through the same stuff at the same time, so you can be objective.
An age difference means that you and your sister experience different stages of life at different times.
With your friends, you typically going through periods of life together, bonding over the struggles and marvels of a particular age: finger paint, Beanie Babies, first kisses, stealing beer from your parents, etc.
But, unless you're twins, you and your sister are at different points in your life, so you can be objective and give each other constructive advice.
3. You bond over the weird/aggravating things your family does.
You and your sister were blessed with the same set of parents, so both you know the minute complexities of your family by heart. Some facts are just too embarrassing to share with your friends.
You were both mortified when your mom was the one to call the other parents at parties in high school.
You've both seen the wrath of your dad when too much is on the credit card bill and you know both think it's strange that he listens to The Indigo Girls.
You share disturbing feelings toward the inappropriate home video of your family vacation to the Bahamas when it resurfaces. You joke about how the family therapist can now put in a pool because of you guys.
You bond over your family's awkward quirks, but at the end of the day, you know they're irreplaceable, and most of what you share is how much you love them.
4. You have different personalities, but you learn from each other.
In friendships, we're often drawn to those who are similar to us.
Good friends have the same sense of humor; they enjoy the same activities and bond over shared interests. But, while sisters can possess the same eye color and facial expressions, they're often starkly different people.
Your sister hates exercise, but running is your escape. Her car is clean as a whistle, but yours is littered with banana peels and gum wrappers.
Sometimes, your sister's life habits and choices are so opposite from your own that it's baffling. But, it's precisely these differences that nourish the sister best friendship because the unspoken promise to support each other is where you learn from each other.
5. She knows your darkest secrets and most shameful habits.
Your sister knows and keeps the secrets you can't tell anyone else — the darkest of the dark.
And, she knows your embarrassing habits, like when you cancel all plans to spend the weekend in a sweatshirt rewatching "Dawson's Creek," eating cereal and wishing Pacey Witter (the master of the mid-sentence kiss) was your real-life boyfriend.
6. She's your go-to girl for brutal honesty.
Should you post the Insta? Does the dress make you look fat? Do you look like you're trying too hard because you're wearing lipstick on a Wednesday?
Your sister is the one who tells you the harsh truth. She'll give it to you straight, sans the sugarcoating. She can't lose you so she has nothing to lose by telling you the brutal truth.
7. You observe the unspoken rule of sister social media behavior.
She's your best friend on Snapchat because you instinctively send her everything you send anyone else, as well as her own personalized snaps (the most unflattering ones).
And, you are obligated to like all of each other's Instagrams. If she hasn't liked it, it means she hasn't seen it, and you can unabashadly text her to go on Insta and double tap STAT.
8. Your relationship can be bipolar.
This happens because you have your guard all the way down. She's family, so you can say anything without the fear of losing her, which means your fights can be really bad.
A tiny argument spirals into a World World III blowout. One second you want to kill her and the next, you'd kill for her.
9. The number-one cause of your fights is clothes.
You can't find your favorite sweater for six months and then, you see your sister wearing it in a picture on Facebook.
What do you do? You lose your sh*t. For some reason, when your sister steals your clothes, it is a million times more aggravating than when a friend does it.
Life was so much easier when your mom made you match.
10. You drunk text each other about how much you love each other.
When you're drunk, you love her even more (if that's possible) and you feel the need to express the depth of your love in long-winded, emotional texts. And, she obviously feels the same, except she loves you more.
11. You require each other's approval.
Your sister's approval is a mandatory component of any significant decision you make.
She's the person who reads important emails before you send them, tells you what dress you should wear to a black-tie dinner and provides you with endless wholehearted advice.
If she disapproves of something in your life, it's for a good reason, and it leads you to rethink things.
12. You two are telepathic.
She knows when you're upset or when there's something you're not telling her, and vice versa. You get each other with a single glance.
Even though you two have different personas, your feelings, reactions and mannerisms are often the same.
13. She's the only one who fully understands and shares your love for the family pets.
You two share a crazy, possibly unhealthy obsession with your dogs and/or cats. The two of you discuss — at length — all of the reasons why you love them.
You understand that they are like real people. They couldn't possibly be any cuter, and your sister is the only one who doesn't think you're insane when you talk about them in strange voices and watch them sleep because they're so cute.
14. If someone wrongs your sister, he or she will have your wrath to deal with.
Your sister means more to you than almost anyone, and if someone hurts her, you feel personally offended and will literally attack him or her and/or ruin his or her life.
15. You have the same values.
Despite your differences, you and your sister live by the same moral code. You trust her judgment and you love all of her best friends.
But, neither of you is perfect, and you call each other out on your faults. You inspire each other to be better people.
16. Your love is unconditional.
Most importantly, your love for your sister is unconditional, the way that love can really only be between children and parents, or siblings.
It's that pure, unbiased, involuntary love that you were stuck with before you even knew her name.
You've experienced life together since the muddled beginning, and even though you're obligated to love her, it doesn't feel like an obligation; she's your best friend and you'd be lost without her.