“I stood for nothing, so I fell for everything”

Katy Perry – Roar Lyrics on LyricsMode
EXPLANATION
She fell for the I's trick (Illuminati) and now she realizes what it is.
EXPLANATION
She is saying that she did whatever she did for nothing and that she was sick of it so she just did what she feels like now.
EXPLANATION
She is trying to say that she didn't exactly feel like she meant anything, "I stood for nothing" Because of this, she never realized that there was a catch, or a trick.