"The Frail" is the third track on the Left disc of The Fragile. The track is an entirely instrumental piano piece (in G Minor) which builds up and prepares the listener for the following song, "The Wretched."
A very simplistic instrumental in two parts, "The Frail" shares its progression with the guitar solo in "The Fragile," and was inspired by the form of Keith Hillebrandt's remix of that track (per its description when it was posted to remix.nin.com). This half-note progression and background chorus synthesizers that appear to be based on samples of Reznor's voice (heard from the end of "The Day The World Went Away") are the sole elements of this song. The piece seems to have been recorded free of a specific tempo. A new, deeper progression and chorus pads seemingly based on (or in tribute to) David Bowie's "Subterraneans" slowly build to a synthesized vocal harmony, leading into "The Wretched."
The Frail (Alternate Version)
Released on The Fragile: Deviations 1. Also known as "The Frail" (Alt) when it was originally released on Apple Music as part of The Fragile Instrumental. This seems to be a different piano performance at an even slower tempo, and lacks any synthesizer layers.
The Frail (Version)
Found on Things Falling Apart, this version contains distorted elements and string instruments, with the melody played on a violin rather than a piano.
The Frail (And All That Could Have Been)
On this live version, Trent Reznor starts by playing the melody solo on a keyboard. There is some improvisation, setting it apart from the album version. As it builds, the other sound elements are incorporated. As on The Fragile, it provides a segue into "The Wretched."
This song is frequently performed live, as on the album, leading into "The Wretched." Reznor has been known to improvise and expand upon the basic piano part in a live setting. More recently, Reznor has occasionally used this song as an intro to "The Good Soldier," "Closer," "Reptile," "La Mer" and "Metal."