A thought

I'm sure you all have heard the phrase "It's not you, it's me," whether it was used on you or on one of your friends or just in a movie. I have a question about that: If it is the person saying this(to me let's pretend) and the relationships ending has nothing to do with me, than she(the speaker) could never have a lasting relationship, as it is always her. Either that or she is lying to me, and really is at least partly my fault.