Because YoonYul does.
“We are YoonYul”
Let’s make this a math theorem shall we?
The YoonYul theorem is a statement proving that YoonHyun, YulSic, and YulTi do not exist. That is, if Yuri is with Yoona, Yuri can not be with Jessica or Tiffany and Yoona can not be with Seohyeon. The YoonYul theorem also runs on correlation to the JeTi theorem (not to be confused with Jedi) used in upper level math.
Proof: UFO from 2009/1/19
Some Dude: What is YoonYul???
Yoona: Real… haha
___
Hahah, I would have owned in Calculus.
YoSooRi!!!! ❤ Best threesome since YoCharMi (Yossi, Charmi(Rika), Miki).
Credit: Aienbest@YT
SNSD Korean 
I LOVE them together <33333
omgs so cute!!!. the hug at the end, it making me what to jump ship….but but YulSic….YoonHyun…. what to do, what to do….
i only understood one word out of the whole 1:28, the word aunt, then they hugged..
cant wait for the subb episode to come out
lol @ sooyoung stealing the spotlight from yoonyul.
lol!! we are yoonyul! how cute x]
i dont know why people keep saying they look alike, i think they both look totally different, a different look which compliments each other to make a perfect match! Yoonaaaaaaaaa~~~
rofl..i would never think of it in that way!
i love it though, the YoonYul theorem and the upper level JeTi theorem..lol.
rofl– yoonyul is most def. real >>> i love how their theorem compromises with the JeTi theorem
-> hahaa YoCharMi was awesome…wasn’t there time when GAM kissed??
lol. they are so cute together! ^_^
YoCharMi!! they were Awesome!
i like all the couples, as long as one of them is real, I’ll be happy!! YoonYul, Jeny, Yulsic
THERE WILL BE NO TALK OF GAM IN HERE! hahaha although I did sorta mention them in another post…
-sLaVe
Haha, I love these two. They come in complaining and get kicked out by Sooyoung and it’s like “You’re taking this from us too!?” Loool. Cute. The hugging was love.
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Yulsic exist xD
Yuri and Jessica sleeps in the same bed… Yuri says her best friend is Jessica
Yoona is a bad friend >.> when Yuri are the best mom in Hello Baby Yoona says: yuri is a traitor
…now
i’m gonna break up with yuri
i been betrayed.totally
…That relationship that we had from the first minute,is all over. (hello baby ep. 6)
and when Yoona is the best mom Yuri hugs Yoona >.>
(hello baby ep. 17)
don’t talk if you don’t see all the ep. xD
YES YULSIC exist and yoona is their child LOOOOOOL XD
To: … If you say that yuri says Jessica is her bestie Jessica also said that yoona was her fab dongsaeng and moreover, yoon a and yuri are sharing a room… So ALL 3 are real; and, since yoonyul made apromise to share kyungsan, it was actually yuri betraying yoona and not the other wat round! You ask ppl to see the show, but have you seen the subs?
Yoona and Yuri make me think of close friends… while Jessica and Yuri make me think of sisters who love each other alot and can be either EXTREMELY CLOSE, just comfortable, or irritated with each other!
for me YULSIC is more entertaining and cuter…
I mean fav dongsaeng and if I misunderstood you, sorry
YoonHyun for me!!!!!!!!!!!!!!!!!!
yulsic is more real… I feel like yoonyul was way over done and just pushed too much… while yulsic was more visible when the camera wasn’t focused on them (you see it off to the side). However I thought it was weird in one episode of hello baby when yoona left and yuri was all like no one else plays with me when yoona is gone (probably because they were so annoyed with their over the top buddy buddiness on camera)… but I don’t know maybe it is real too… ah! but I mean people can have more than one best friend… I just love yulsic the most!
ah! i love yulsic more than yoonyul… but i also love jeti… ah! anything with jessica really!
WELL SAID!! im a YoonYul Shipper! and im totally dont like YulSic and Yoonhyun.. because YoonYul is real..keke
kekeke, people so worked up for this shipping things… I like yoonsic better actually, just because yoona n jessica seem so close since their training days, lol… All pairings are real (in shipper’s mind) but if you wake up (literaly) you’ll realize that’s what we call soshi bond… Cause all the girls still dreaming to marry a good man…maybe that’s the reason for sm forbade their artists to involve in any kind of romantic relationship
wow…gr8!! yoonyul=reality
i love yoonhyun foreverrrrrrrr.
yoonyul is real!!!!!! i fell like sica is stealing yuri away from yoona!!!! yoona and yuri are bff 4ever!!!!!! hate yulsic…… stupid yulsic!!!!!
YOOOOOOYUL IS REAL!!!!!!!!! i fell like yulsic is wayyyy over done!!!!!!!! yulsic is not real and it will never be!!!!! the only reason why yoona yuri are roomates is cuz they are best freinds!!!!!! bye yulsic….. never come back!!!!!
ummmm…….. hello??? yoonyul is real!!!! pay attention to them….. they do every thing together!!!! yulsic stinks!!!!! im soooooooooooooo sorry yulsic fans but sica needs to stay with fany and yoona needs to stay with yuri!!!!!!!!!!!!!
dont u seee????? yuri and sica r just friends…… i feel like sica is just being mean and to yoona and trying to steal yuri away from yoona but yuri loves yoona…….
yoonyul is real and yulsic is stupidddddd!!!!! yulsic fan r stupid tooooo!!!!!!!!!!!! haha
yulsic is not real………..not trying to be me mean but i dont like sic….. i bet yuri doesnt too sooooooooooo she is trying to avoid her a want yoona to be next to her now!!!!!!!!
omg yulsic is the worst…. yoonyul is the best…. my fave is sica though but i just dont think sica and yuri are bestfriends like yuri and yoona….
Now either are doing that well LOL
although I’m a hardcore yoonyul shipper, I kind of feel rather bad that yulsic is totally dead now (read again: YES, TOTALLY DEAD). They’re not like the second taengsic (they’re still close) but not as close as 2009-2012.
Yoonyul too, sadly.
I see lots of Yulti, Yoonsic, Hyoyul and Soori this year.
Not that is a bad thing, but my OTP is broken up :-; yes, there has been many fancam moments of yoonyul which is why im still a shipper, but to put it in a nutshell, there isn’t as many as there was in 2008-2009. But there were an abundance of yoonyul moments the wow o_o
So anyway, bottom line is, just believe in yoonyul 🙂 ❤