In his book, Wasserman repeatedly emphasizes that those two lines originated verbatim in his original teleplay, and generally laments the lot of the librettist. He writes:
It works like this: I, the "bookwriter" wrote, "To dream the impossible dream, to fight the unbeatable foe..." The lyricist then wrote:
To dream the impossible dream,
to fight the unbeatable foe...
— whereupon, through the alchemy of contractual usage the words became his forever.
Later, Wasserman elaborates on this:
Once upon a time I invented a phrase, "the impossible dream." People think it comes from a song, but it doesn't. It's from my original television play, "I, Don Quixote". The phrase has gone into the language and traveled far and wide. It's been used (and abused) countless times, and will continue into the future. I invented it simply to explain Don Quixote's quest — indeed, the song's proper title is "The Quest." But the public seized upon the eponymous phrase and won't let go.
...Sometimes I'm sorry I invented it. Sometimes I feel I opened a verbal Pandora's box and wish it could be slammed shut again.
Poor Wasserman. It must have been quite a burden for him. Of course, it would be much easier to sympathize with him IF HE HAD ACTUALLY INVENTED THE PHRASE. Thanks to the research of Dr. Howard Mancing, Professor of Spanish at Purdue University, we know that the lines "To dream the impossible dream, to fight the unbeatable foe" actually originated in the press materials at the back of the Samuel French publication of Paul Kester's 1908 play, "Don Quixote". Here's a 2008 news report dating from the month before Wasserman's death, that tells the story:
I wondered if it was possible that the script Mancing found might have been a later edition, and so the press materials were actually quoting the musical. I contacted Samuel French — they didn't know anything about the whole affair — and I heard back from two very helpful and interested employees. The script was long out of print, but one of the employees sent me a PDF of the entire thing. After examining it, it is unquestionable to me that the publication dates back to 1930, no later.
It's already pretty "impossible" to believe Wasserman's claim that he came up with the exact same ten sequential words, all on his own. But wait: There's more! Wasserman's Wikipedia page mentions that the phrase "To each his Dulcinea" appears in Kester's play as well. (I'm guessing this information stems from Mancing's research too, but I'm not certain.) "To Each His Dulcinea" is a song in "La Mancha", sung by the Padre.
Sure enough, there it is on page 30 of Kester's script:
PRIEST. (Smiling sadly) To each his Dulcinea!
Wasserman included his "I, Don Quixote" teleplay at the end of "The Impossible Musical". And lo and behold, on page 263 of that book, what do we find?
PADRE (A pause. With a sad smile:) To each his Dulcinea.
Wasserman borrowed not only the exact line, but also the sad smile!
And really, it's fine that he appropriated these words. It's inarguable that on the whole, Wasserman used Cervantes' novel as a springboard for his own original work. But his vehement, angry, defensive emailed denials in the video are still troubling. Someone with a lot of time and interest should study first Cervantes' novel, then Kester's play, then Wasserman's teleplay, and finally the "La Mancha" script, to see just how much of a debt Wasserman owes to Kester. It sounds like a most interesting Quest.