My interpretation of this song is mainly that she, like everyone else, was told to be careful and protect her heart, don't give it away too easily. But once she met this guy she fell head over heels, gave in, and lowered her walls, only to prove everyone whoever cautioned her, right. It seems she's telling the guy who broke her heart, 'yeah you got me, go ahead and tell everyone how you taught me a lesson, how now I really know what it's like to feel a broken heart.' Great lyrics:). Song Meaning'Impossible' is a song about a girl who decided she would take wise advice and apply it to her life while taking 'caution when it comes to love.' And so she did, and everything seemed perfect for the long run. But further into their relationship, it was clear that her significant other was stronger than her in the relationship, 'you were strong and I was not' and because she was so deep in love with him, she was 'careless and forgot' about continuing to take caution, or realizing that he was in total control.
This completely damaged their relationship because he took advantage of her naiveness about love and trust. 'You have gone and so effortlessly You have won' this is referring to the fact that he broke her heart so easily, with a snap of his fingers, by cheating on her with multiple women. 'Tell THEM all I know now' is her wanting the other women to know because if her relationship to him meant nothing, than neither will his other ones. 'Tell them what I hoped would be impossible' He is never going to change because as the saying goes. Once a cheater, always a cheater. It's a lifestyle he's grown into and it was impossible for their 'love' to mean anything when she wasn't the only girl in his life.