According to a study done by the people at the Around the World Survey (and presented in brief detail in Readers Digest), a signficant portion of married people would not marry their spouse if they could do it over again.
"On average, 68% of respondents in 15 countries would again say "I do" to their spouse. In the United States, respondents over 45 are more likely than younger people to feel satisfied with their choices."
To the question: "Would you marry the same person again?" here are the responses of "YES" by country...
United States 63%
Check the U.S. figure. That essentially means that 37% (or more than a third) of us would do something different if given the chance. I suppose that's what we see in our out of control divorce rates.
Remember, if the grass seems greener on the other side of the fence, it's often because there's more poop over there.