After the tumultuous hiatus, the band reunited for 1999's No. 4. The band decided to return to heavy roots - on many of its tracks, most notably first single, "Down". But the album also featured the gentle, largely acoustic single "Sour Girl".
Scott Weiland wrote the song about his first wife, Janina Castaneda. They got married in 1994, as Stone Temple Pilots were becoming one of the biggest bands in America. Weiland admitted that he put her through hell with his capricious behavior that stemmed from his addictions. "Everyone is convinced that it's about my romance with Mary [Forsberg, second wife]," Weiland writes in his autobiography Not Dead and Not For Sale. "But everyone is wrong. 'Sour Girl' was written after the collapse of my relationship with Jannina [Castaneda, first wife]. It's about her. 'She was a sour girl the day that she met me,' I wrote. 'She was a happy girl the day she left me… I was a superman, but looks are deceiving. The rollercoaster ride's a lonely one. I pay a ransom note to stop it from steaming.' The ransom note, of course, was the fortune our divorce was costing me. And the happy state, which I presumed to be Jannina's mood, was because she had finally rid her life of a man who had never been faithful." "Sour Girl" also appears on the compilation albums Thank You and Buy This. It was the only Stone Temple Pilots song from No. 4 to reach the Billboard Hot 100, where it peaked at number 78.
"Sour Girl" was one of STP's biggest hits since the Core and Purple era. Billboard ranked "Sour Girl" at #88 on its list of the 100 Best Rock Songs of the 2000s. The song peaked at number four on the BillboardMainstream Rock Tracks chart and number three on the BillboardModern Rock Tracks chart.