In arranged marriages, you parents don't team you up with a stranger. So chances of you being married to a wacko are pretty slim.
Usually, during your adolescence, you meet this person (if you don't already know them) and, sometimes, you can go on parent-approved outings with them (very rare). Or you won't meet until the wedding day.
I think arranged marriages are harder because you have to make an effort to get to know that person. There is no, "I wonder if I am compatible with this person," or "Even though I've known you for several years before we chose to get married, things aren't as I thought they'd be and I want a divorce." You're already with them so you have to make it work and I think, because of this (and social norms), arranged marriages are more successful.
Why is it that people who choose marriage can't handle it, while those who have no choice up hold it?
When we have no way out of things, we try our hardest to endure (think school work, job responsibilities, etc). But when we have leeway, we tend to "escape" when things get rough.