However in this case normal distributions do NOT apply. There is significant financial pressure put on men to make them stay in the marriage even though they don't want to. If you take that away, I think you're probably looking at 10% or less are truly happy.Stats are hard to come by, but
( http://www.buzzfeed.com/annanorth/divorce-author-i-think-17-of-marriages-are-happ )
This agrees with a number (20%) that I read about years ago in a study of long term marriages - of those still together after 20+ years, about a fifth are quite happy in their marriages. That implies most range from very unhappy to content, and if normal distributions apply, then the majority are in the "good enough to stay and not bad enough to leave" category.