No singles were released from Kid A, but promos of several songs from the album, including "Optimistic", were sent to radio stations. Without an official single specified by the band or label, the guitar-driven "Optimistic" became the default track to be picked up by alternative rock stations and received more airplay than any other track on Kid A. The song hit #10 on the Billboard Modern Rock charts
"Optimistic" was performed often during an initial tour in 2000 but it did not appear again in Radiohead's live shows until it was brought back in 2008 to be played twice at a special show for BBC Radio 1 on April 1 , and again on May 4, during a VH1 exclusive concert at the Basement, London, featuring a set from their newest album In Rainbows. It has now become a regular part of the setlist on their 2008 tour. The live performance is similar to the one found on the album, featuring guitar, bass, drums, and ondes martenot, an electronic instrument played by guitarist Jonny Greenwood.
The chorus for "Optimistic" was directly inspired by Thom Yorke's long term partner. During the making of "Kid A", Thom was constantly stressed and on the verge of an emotional breakdown because of his desire to make the album as perfect as humanly possible. His partner would constantly try to calm him down by telling him that, "the best you can is good enough". The lyrics of the song also reference George Orwell's Animal Farm.