Imagine being taught a new song only to have it be ever changing, so that just when you think you have it learned, the person teaching you the song comes in and changes virtually everything you've just been taught about it.
That's exactly what happened in early 1968 right around the time David Gilmour joined Pink Floyd. Gilmour had been a friend of Syd Barrett since childhood, and had become very aware of Barrett's progression into a hermetic lifestyle. While once a prolific songwriter and composer, Barrett had become completely indulgent on LSD and his status within the band was quickly diminishing. It got to a point where IF Barrett would show up at a gig, he'd wander around the stage, only occasionally picking up a guitar and being a part of the group. He became a sideshow, which the audiences loved, but the band began to resent it.
Appearing with Pink Floyd on Dick Clark's American Bandstand, Barrett became terse while answering questions, coming off as rude. As a guest on Pat Boone's show, he ignored questions all together and just offered a mute stare into the camera lens, refusing to say anything at all. Nick Mason later said, "Syd wasn't into moving his lips that day."
The other band members eventually had enough of Barrett's antics and, in January of 1968, when Roger Waters was driving on the way to a show at Southampton University, the band elected not to pick Barrett up.
One person in the car said, "Shall we pick Syd up?" and another said, "Let's not bother." Up until then, Barrett had been the primary composer of the band's material, and the initial plan was to keep him in the group as a non-touring member - as The Beach Boys had done with Brian Wilson - but this soon proved to be impractical. Gilmour subsequently became a full-time member of the band, replacing Barrett on guitar and vocals.
The Mad Hatter got the last laugh however. According to Waters, Barrett came into what would be their last rehearsal session together with a new song. He was calling it, "Have You Got It Yet?," and the first couple times they ran through it, it seemed simple enough. Soon the band realized that the song wasn't simple at all - Barrett would change the melody and the arrangement constantly with each new practice run - slightly at first, but more and more each time they played it. Barrett would play it again for them, with the capricious structure changes, and each time he would ask, "Have you got it yet?"
Of course, the band never did quite get it, as they were chasing the proverbial carrot on the string. Eventually they realized that they had become victims of Barrett's eccentric sense of humor. In fact Waters stated, in an interview for The Pink Floyd and Syd Barrett Story, that upon realizing Barrett was deliberately making the tune impossible to learn, he put down his bass guitar, left the room, and never attempted to play with Barrett again. Waters had called it "a real act of mad genius".
The song was never recorded by Pink Floyd or Syd Barrett.