Well, that's the trick, isn't it, in the very practical sense? I mean - I don't think anyone goes into marriage thinking "Gosh, I'm just gonna give this a shot and see how it goes. But if it isn't what I thought it was going to be then I'll divorce."
I think most people go into marriage sincerely believing they're going to make it work, have the maturity to do so, etc. But, people have an alarming tendency to misread themselves and what they're capable of. It's kind of like the stories you hear about how the most "gung ho" guys get into battle in war - and turn out to be the first ones to get killed off because they freeze/etc. You often really don't know what you're gonna do until you're truly faced with a situation.
...and you REALLY don't know what someone else is gonna do.
So in a sense - it is kind of a crap shoot. It's all well and good to talk about "make sure you marry someone who's committed to the marriage" - but you REALLY don't know until you're sitting there with a crappy situation where you've got overdue bills piled up while the kid is screaming until 4am and you haven't slept in 2 days. You really don't know until you've told your last story about growing up for the fifth time over the past 10 years and they're looking at you annoyed that you told it again...etc..etc.
That's when you truly find out what a person is all about.
I was talking to my wife's aunt the other day who's in the midst of a divorce... She was telling me what a pain the guy is being, how he's calling her names, how he's doing this, how he's doing that, how he was in the marriage, how he was abusive, etc... and then she goes "He's a nice guy, and I feel sorry for him."
My response was "What do you mean he's a nice guy? Do nice guys do the list of things you've iterated out?"
"Well, he's just reacting because he feels hurt. If you're on his good side he'll do anything for you."
Well - isn't that the thing, though? Isn't the measure of someone what they do when things suck? Everyone is good when things are going swimmingly and how they want them to go. You don't get any bonus points for that in my eyes. The test of a person is how graceful they are through crappy situations, IMHO.
Same thing goes in marriage. I think the idea of "marrying well" is a noble idea, and there are things that you ought do in order to do your due diligence...but...when it really comes down to it - the truth is that it *IS* a crap shoot and far more random than people like to believe it is. Everyone has romanticized ideas about themselves and who they are...but that's usually a bunch of nonsense. Sure, there's a degree of truth to it because people at least try to be what they aspire to. But, when the tires hit the pavement, and when things draw on, that's when you see what you really have (and what you truly are).
IMHO.