Because this song has three chords
It's easy
Because this song has three chords it's not new
I hear every garage band play it too

The jam starts on an A chord
Two measures
It goes up to a D then along the way
You finish up with E return to A

(everybody trades solos)

I hear it when the guys don't know
A damn song
I hear it when the band's been drinking booze
I guess that's why it's called a twelve bar blues

(More solos)

There's no real words you just make up
The lyrics
It doesn't take a decent voice to sing
You play it when the band don't know a thing