Dating & Marriage, Part 4--Footnote

Coincidently enough, Times & Seaons is having a discussion on divorce currently, which fits right in with the Dating & Marriage theme of this series.  (My series discussion of divorce is forthcoming...)

The comments from T&S mention a quote from Spencer W. Kimball which I had saved for later, but might work better now as a footnote:

While marriage is difficult, and discordant and frustrated marriages are common, yet real, lasting happiness is possible, and marriage can be more an exultant ecstasy than the human mind can conceive. This is within the reach of every couple, every person. "Soulmates" are fiction and an illusion; and while every young man and young woman will seek with all diligence and prayerfulness to find a mate with whom life can be most compatible and beautiful, yet it is certain that almost any good man and any good woman can have happiness and a successful marriage if both are willing to pay the price. -- Teachings of Spencer W. Kimball (1982) pg. 306

Note that Pres. Kimball discounts "The One" theory just as I do.  Also of note is his statement in the last sentence which supports my Working Theory #2: All marriages can succeed

Wait, though...he very specifically said 'almost any good man and any good woman'--implying that there are combinations which inherently cannot create a successful marriage.

I can't think of what those would be, though...   Far be it from me to presume to intrepret the words of a prophet, but I think he may have used 'almost' here just because of human nature--it's natural to automatically 'qualify' statements so as to avoid absolute words such as 'always' or 'never'.  It's common to stick 'almost always' or 'usually' instead of 'always'--and 'rarely' instead of 'never'--just because in most things it's easy to find at least one exception somewhere even if you can't think of one at the time.  (This saves embarrassment from hearing about--or thinking of--an obvious exception later...)

Pres. Kimball might have had a specific situation in mind for his use of 'almost', but the original source doesn't say what that might be, so I think it's possible he used 'almost' here in the sense that he's allowing for the possibility that an exception exists, but can't think of what that would be (I can't think of one, either...).

In a sense, the 'almost' is redundant, since the last phrase "IF both are willing to pay the price" acts as a pretty good qualifier by itself.   Of course, any marriage can fail if one or both aren't willing to do what it takes...but is there really a situation where a marriage will still fail even with both partners doing everything they can? (and I mean everything...)

Open questions for discussion, then:
(1) If Working Theory #2 is false--what characteristic or circumstance of one or both partners can you think of that would prevent the marriage from ever being 'happy' or 'successful' (however you want to define those terms...)  Remember, this is inherently flawed--not because of the actions of one or the other...
(2) Even though the focus of the series is on LDS marriages--does Working Theory #2 apply to all marriages, also?  In other words, if you have a devout Mormon, and a devout Muslim married to each other, for example, is this situation (or any other one you can think of) still capable of achieving happiness?  If not, why not?