I've gone over this before, most deeply with Dr. Dre producer Dawuan Parker, but the biggest lesson I've learned as I've moved beyond this here keyboard and started getting the occasional peak into how the music industry works, is that it's completely balls crazy.
Before I started hearing stories from artists, songwriters and producers, I assumed the flow between a song being written and landing on an album was a carefully constructed, deliberate process. Producer A gets in the studio with Artist A, Artist A selects the song for their album, all the paperwork and legal shit gets worked out, marketing plans are developed, and then the album drops. And to be sure, that does occasionally happen, but most of the time? Not even close. The music industry essentially operates on some MacGyver shit - billion dollar labels are essentially held together by rubberbands and paper clips.
Case in point, Eminem and Rihanna's mega-uber smash shit, "Monster", which has already sold well over two million copies and will go down as one of, if not the, biggest hits of Em's stellar career.