A MacGuffin (sometimes McGuffin or maguffin) is:
A plot element that catches the viewers' attention or drives the plot of a work of fiction. The defining aspect of a MacGuffin is that the major players in the story are (at least initially) willing to do and sacrifice almost anything to obtain it, regardless of what the MacGuffin actually is. In fact, the specific nature of the MacGuffin may be ambiguous, undefined, generic, left open to interpretation or otherwise completely unimportant to the plot. Common examples are money, victory, glory, survival, a source of power, or a potential threat, or it may simply be something entirely unexplained.
The MacGuffin is common in films, especially thrillers. Commonly, though not always, the MacGuffin is the central focus of the film in the first act, and then declines in importance as the struggles and motivations of characters play out. It may come back into play at the climax of the story, but sometimes the MacGuffin is actually forgotten by the end of the film.
The director and producer Alfred Hitchcock popularized both the term "MacGuffin" and the technique, with his 1935 film The 39 Steps... "In crook stories it is almost always the necklace and in spy stories it is most always the papers."
Blocked writers tend to obsess over these problems, but none have any importance in productive work, where your goal should only be to put one word ahead of another. They are merely stand-ins and distractions.
A perfectionist MacGuffin is a word or concept that your perfectionism has found is particularly triggering for you, and so it starts using that word as a club to bash you with whenever you feel emboldened to write. Just like a film MacGuffin, a writing MacGuffin seems like the most important thing in the world, but it is a meaningless distraction from the real issue: fear.
Here's some facts about specific categories of MacGuffins:
"Quality," "authenticity," etc., are achieved not by maintaining a Nazilike vigilance over your work (which will only intensify your block), but via an incremental and free writing process. You are already imbued with quality and authenticity and all the other qualities you need for your writing -- they come from your reading, learning and life -- and if you write without barriers they will manifest themselves. As for those areas where you are weak -- we all have them -- you can get support from editors, agents, and critique buddies.
As for "originality," all of the above also applies and, well, hell, even Shakespeare borrowed some of his plots.
"Talent." The biggest MacGuffin of all:
From Brenda Ueland: "Everybody is talented because everyone who is human has something to express." (The next section of her book is, "Everybody is original.")
From Stephen King: "Talent is cheaper than table salt. What separates the talented individual from the successful one is a lot of hard work."
From Erica Jong: "Everyone has talent. What is rare is the courage to follow the talent to the dark place where it leads."
From David Bayles and Ted Orland's Art and Fear: "The conventional wisdom here is that while "craft" can be taught, "art" remains a magical gift bestowed only by the gods. Not so... Even talent is rarely distinguishable, over the long run, from perseverance and lots of hard work."
Albert Einstein (why not? It's a great quote, and he was also a writer.): "I know quite certainly that I myself have no special talent; curiosity, obsession and dogged endurance, combined with self-criticism, have brought me to my ideas."
Nothing is a bigger waste of time than to worry about whether you have enough talent.
Credentials. My "favorite" MacGuffin in that it's the least legitimate concern of all. Some people feel huge illegitimacy around their degrees or other credentials or, perhaps more accurately, they feel illegitimate to start with and use credentials as a confirmation of that feeling -- feelings of illegitimacy and fraudulence are rampant among perfectionists -- but a degree by itself is meaningless. What's important is that you've had good teaching and mentoring; and, the truth is, it is very possible to get those without getting an expensive degree.
Perhaps I'm influenced by my high tech background (Bill Gates and Steve Jobs were both college dropouts) or my business background (businesspeople tend to be less concerned with who you are than with what you can do for them), but I find credentials an archaic, 20th century concern. Obviously, you need them for some fields (surgery, anyone?), but do you really need them for writing? I don't think so.
Bottom line: if you're obsessing over a particular element of your writing, it's probably a MacGuffen.