1. Convincing your mom and dad that one of you deserves to get her ears pierced already.
2. Deciding that it’s time for one or both of you to start shaving her legs, and figuring out the hard way how to do it without drawing blood.
3. Doing each other’s nails and makeup because impromptu makeovers are a surefire way to stave off boredom at any age.
4. Crushing on the same male characters from all the TV shows and movies you watch together.
5. Laughing at the exact same moments during any movie or TV program, knowing on some level that your shared sense of humor is a result of your parallel experiences as females in this world.
6. Discussing each other’s real life crushes and swearing each other to secrecy about any related fantasies.
7. Having so many inside jokes that you practically speak your own language.
8. Insulting each other with the lowest of low blows because you know each other inside and out, weaknesses included.
9. Learning to forgive and forget through being total mean girls to each other but getting over it quickly, no matter how serious the crime.
10. Understanding early on that being copied is the sincerest form of flattery because there’s no better feeling than being mimicked by your sister. Catching her dress like you and/or talk like you makes you feel beyond proud.
11. Fantasizing together about what life would be like as identical twins, a la Sweet Valley High or Mary-Kate and Ashley.
12. Discussing what it will be like to have boobs and to wear a bra one day.
13. Reminiscing, eventually, about how you used to stuff bunches of tissues down your shirts and parade in front of the bathroom mirror while wondering what actual boobs might feel like.
14. Answering each other’s questions about menstruation. Namely, how much period blood there will be, exactly, and whether or not sticking a tampon up your vagina will hurt at all.
15. Nodding and smiling throughout whatever sex talk your parents give, knowing that you’ll get way more useful answers by consulting each other.
16. The specific joy that comes with being able to share clothes and to essentially have two wardrobes.
17. The special brand of hate that brews when your sister borrows something without asking you first.
18. Plotting your sister’s downfall after she ruins one of your favorite tops but forgiving her before you have the chance to pursue whatever vengeful plan you conjure.
19. Telling your parents to chill as they worry because your sister’s running late from a date.
20. Taking your sister’s side as your parents scold her for breaking curfew or for failing to check in like she promised while out with friends or some guy she wants to boyfriend.
21. Ganging up on your parents to change a longstanding household rule about dating, or to get something you both desperately want, like a dog, or a new computer.
22. Defending your sister’s honor if anyone dares to say anything rude about her because you’re the only one who’s allowed to make fun of her.
23. Being known by every teacher and most people in school as your sister’s sister.
24. Love-hating the assumptions people make about you as a result of associating you automatically with her.
25. Comparing yourself to your sister in literally everything you do (because everyone else seems to) so that life feels like an ongoing, borderline friendly competition.
26. Failing to relate to the fear of being single because you have your sister to love and lean on at all times.
27. Feeling relieved because you don’t have to choose a friend to be your maid of honor since you have a sister to fill that role.
28. Toasting each other’s awesomeness at your respective weddings.
29. Discussing exactly how you’ll do things differently from the way your mother did.
30. Laughing over all the evidence that you’re both clearly turning into your mom in spite of all your efforts not to.