I'm not exactly a hipster. But I do know a lot of hipsters. So here I'm going to explain why I think hipsters always say "I knew that before it was popular."
I think it's a sense of possession. We humans like to own things, and I think that if you own something that nobody else owns, it's very special. It's especially obvious when you're young. That doll that your mother made for you was even more special than the one bought from the store. That awesome treehouse that you have in the back yard is the coolest thing ever.
But hipsters own something that is available to the public. They listen to music that everyone can access on iTunes or whatnot, but everyone doesn't, because they don't know about it. So this makes the music special. It's their own very special music.
Then the music becomes popular. This is the most terrible thing that can happen from the perspective of a hipster. Now that the music is popular, it's not as valuable anymore, because people know about it. And then it gets played on the radio (not even the best songs on the album, just a select few, which personally bugs me) and it's lost its magic. Then the hipsters stop listening to it because it's lost its value, and then they have to go find music that nobody knows about and then the cycle starts all over again. And whenever you hear that song from that band that nobody knew about six months ago on the radio, you shake your head because you knew it before it was popular and now surely their music is going to be really bad from now on because fame is going to go to their heads. It's tragic, really.
Oh, and then there are those people who call themselves "fans" of the band even though they only know the one song that's being played on the radio.
Because I am sort of a hipster, I am going to say a few things:
I knew Imagine Dragons before they were popular.
AND FOR GOODNESS SAKES I KNEW OF MONSTERS AND MEN BEFORE THEY WERE POPULAR. I STARTED LISTENING TO THEM LAST MARCH OR APRIL. But I still listen to them even though they're well known now because their music is really good. Though I still believe that Little Talks is not their best song.