Condon supported the view that similarity was important in terms of romantic relationship formation from the way that we assume that people similar to us will be more likely to like us which lessens the chances of rejection. Furthermore, when other people share our attitudes and beliefs, it tends to validate them, which in turn is rewarding and this relates to the reward/need satisfaction theory. However, Rosenbaum suggested that dissimilarity rather than similarity was the important factor in determining whether a relationship will develop. This dissimilarity-repulsion hypothesis has been tested in as number of different cultures e.g. Singh & Tan in Singapore, and Drigotas in the USA.

These studies established that participants were first attracted to each other because of similarity of attitudes, and that, as they got to know each other better, those who discovered more dissimilarities than similarities became less attracted to each other.On the other hand, some psychologists have argued that research into similarity and dissimilarity has its limitations as they have only dealt with attitude and personality similarities. Yoshida pointed out that this represents only a very narrow view of factors important in relationship formation, with factors such as similarity of self-concept, economic level and physical condition being equally important. For example, research by Speakman et al. found that people often choose partners with similar levels of body fat.Most of the studies carried out in this area are laboratory studies and therefore do not necessarily show that the principles of need satisfaction and similarity apply to real life, thus, lacking in mundane realism/ However, some studies have been conducted on real-life couple, and have tended to support these claims (Caspi and Herbener).