1. Knowing each other's tendencies and tricks.

Growing up together, you get to know each other's tendencies. Whether it's alligator tears, faking being sick, or anything else, you can see right through it. My sister and I used to wrestle, and whenever she pinned me down I would yell that I would have to go to the bathroom, and whenever she was pinned down, she would pretend to be passed out. While these worked for a while, we figured each other out and never were fooled by those tricks again.

2. Clear maids of honor

Every little girl thinks about their wedding, and what better person to be the maid of honor than the one who has been with you every step of the way? Your sister is your literal day one. Sister relationships are important, and you should be there for each other through every major life event.

3. Being called the wrong name.

This happens to all of us little sisters. We may have some of the same teachers as our older siblings, and they call you your sister's name without even thinking. They might apologize and say it's because the two of you look alike, but now you just tune it out. You eventually are conditioned to respond to both names.

4. Being in sync at all times.

Sisters typically spend a lot of time together. This might result in learning to do the perfect duet to Disney songs, having the same exact morning routine, or getting hungry at the same time. If you spend enough time together, it will eventually feel like you are the same person.

5. Borrowing each other's things.

One of the awesome things about having a sister? Double wardrobe! If you are lucky enough to have the same clothes or shoe size, you are definitely taking advantage of that. Headbands, jewelry, makeup, etc. is all fair game.

6. Similar music taste.

My sister was born in the early 90s and grew up on NSYNC. Though I was only 4 years old when NSYNC announced a "temporary hiatus," I also grew up listening to NSYNC, and it was always something we listened to together. Even with more modern musical artists, we tend to gravitate to the same musicians and genres.

7. Christmas card pictures.

If you have a sister, or any siblings for that matter, you probably had some Christmas card pictures done at some point. No matter what the age, you had coordinated matching outfits that only really looked good on one of you.