"Presented with a song like Exit Music, It's impossible to know what to add without actually making it worse. How can you play along when It's already there?"

In this quote, Jonny Greenwood is revealing the problem of contributing to a song that is currently total and perfect, such as "Exit Music." He acknowledges that it is impossible to understand what to include without potentially destroying the tune. He questions how one can contribute to a piece of music that is currently so well-crafted and present. It is a predicament that lots of artists deal with when working together or covering a song. Greenwood's words highlight the fragile balance between including one's own touch to a song while also appreciating and maintaining its original essence. It serves as a suggestion to value and honor the art that currently exists.