In the Talmud Yebamot 63a the Rabbis gave many advices on the issue of shidukhim (=finding your spouse. See here). One of them is: "nachit chad darga unsib iteta." Descend one step to find a wife". What did they mean by that?
I will present two interpretations.
The first, based on Rashi's commentary, views these 'steps' as socio-economic steps and focuses on one aspect of married life: financial differences between husband and wife. A man who himself does not come from a rich family might be tempted to look for a spouse that comes from a wealthy family. What he might overlook is that, generally speaking, a woman's natural expectation is to upgrade or at least maintain her financial status once she gets married. A woman that as a daughter was raised with luxury, being able to afford not only what she needs but also what she wants, will not easily adapt to a lower lifestyle. Soon the differences might come up. Items that her husband considers them as luxurious extravagances, for her are part of her normal lifestyle or a matter of need. Although people change (and many people easily adjust to lower financial situation) the appreciation of what we have depends in great part on what we used to have.
To avoid this type of financial tensions the rabbis--two thousand years ago--gave this practical advice: when looking for a wife, don't look one step above you. You might not be able to meet your wife's material's expectations.
Instead, they said, "look one step below your own socio-economic level, and take a wife". That, at least in the material aspect, will be a win/win. Your wife feels that she has upgraded herself financially with you (haisha 'ola 'im ba'alah), and a lifestyle that for you is normal and affordable, for her will be a luxury! Everyone is happy.
For a different perspective on this issue READ Financial inequity . Her parents have more money to give. Does that create a problem? by Rosie Einhorn, L.C.S.W. and Sherry Zimmerman, J.D., M.Sc. (From Aish.com)