People change in a marriage -- that's often cited as a reason for family breakdowns, but it's equally true of the best, not only lasting but thriving marriages, Tara Parker-Pope in the New York Times points out, reporting on the work of three scholars at universities in New York, New Jersey and the Netherlands.
Parker-Pope take pains to emphasize that while self-fulfillment is key to satisfying, lifelong marriages in modern times, that self-fulfillment is not purely selfish or hedonistic -- a good marriage improves each partner morally and ethically, may make them more effective and productive, and increases each person's variety of social connections, through which they give as well as receive benefits.
On stories like this, the headlines, which vary as it is reprinted in papers around the country, will often dumb down and overstate the point. This factor is not necessarily the only thing that makes a marriage worthwhile; it doesn't displace everything else we know about marital quality, strength and health (e.g., if you are new to this discussion, see www.smartmarriages.com). But it's important and all too often forgotten. Sometimes qualities are not talked about unless they can be quantified, which makes us over-emphasise the more quantifiable or more often-quantified things. The researchers quoted in Parker-Pope's story have found ways to quantify and study this self-expansion factor, including a quiz measuring self-expansion that anyone can take online.