Many couples feel that their relationships do not live up to their hopes and dreams, especially as the realities of routines, disagreements, and natural differences in personality set in. (relationship-center-mi.com)
The discrimination is based on natural differences, not differences in views. (religion.blogs.cnn.com)
Because researchers are not intervening for purposes of the study they can not control natural differences that could explain study findings so they can not prove a cause - and - effect relationship. (sciencedaily.com)