I believe this song is possibly the darkest of U2 songs. Bono stated at Apple these songs were about life in Dublin growing up, relationships with friends, family and "lovers". This song is a dark and unquestionable admission to infidelity. An affair that went to far and too deep by one of the band members. Someone was lured by someone else's pain, fell into love with that person... realizing the troubles that this person had created for them was in fact a trouble in themselves. Knowing your own tricks is the hardest thing you ever do.
Michael Meldeau meldeaulive.com (16th of September 2014)