From Lafcalio Hearn's "In Ghostly Japan":

[...]From very ancient times, the writing of short poems has been practiced in Japan even more as a moral duty than as a mere literary art. The old ethical teaching was somewhat like this:-

"Are you very angry?-- do not say anything unkind, but compose a poem. Is your best-beloved dead?-- do not yield to useless grief, but try to calm your mind by making a poem. Are you troubled because you are about to die, leaving so many things unfinished?-- be brave, and write a poem on death! Whatever injustice or misfortune disturbs you, put aside your resentment or your sorrow as soon as possible, and write a few lines of sober and elegant verse for a moral exercise."

Accordingly, in the old days, every form of trouble was encountered with a poem.[...]

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( MY TOS:KOR FAIL, LET ME SHOW U IT. )

( Bump of Chicken: Hammer Song and the Tower of Pain )

Lyrics and translation source, along with a more detailed explanation of the song.
Another version of the PV and a Reborn ver.