In late 1955 when the Broadway show My Fair Lady first went into rehearsal, there were two immediate problems. One was that Julie Andrews, who originated the role of Eliza in the musical, couldn't master an acceptable Cockney accent. She could sing and speak beautifully as Eliza after the character had been coached in linguistics by Henry Higgins…but she spoke too well to be convincing in the early parts where Eliza hadn't yet learned to speak like a lady.
It was so bad that at one point, Rex Harrison — cast as Higgins — refused to rehearse any longer with her. He declared it a waste of time as Ms. Andrews would certainly need to be replaced in the part. Eventually though, she mastered it.
The other immediate problem was that Mr. Harrison, who'd never appeared before in a musical, could not sing with the full orchestra. It terrified him and it also insisted on playing the tunes as per the sheet music, whereas he never sang one of his numbers the same way twice. As with his co-star, he finally got the hang of it and My Fair Lady went on to become a smash hit and one of the most honored stage productions of all time.
In early 1960, Andrews and Harrison agreed to be very good sports and to appear on a CBS TV special and "re-create" scenes from those early rehearsals, telling the world how terrible they were during the show's formative weeks. Thanks to my friend Vince Waldron for letting me know about this…