Principles of similarity and complementarity seem to be contradictory on the surface (Posavac, 1971; Klohnen & Mendelsohn, 1998). In fact, they agree on the dimension of warmth. Both principles state that friendly people would prefer friendly partners. (Dryer & Horowitz, 1997)

The importance of similarity and complementarity may depend on the stage of the relationship. Similarity seems to carry considerable weight in initial attraction, while complementarity assumes importance as the relationship develops over time (Vinacke, Shannon, Palazzo, Balsavage, et-al, 1988). Markey (2007) found that people would be more satisfied with their relationship if their partners differed from them, at least, in terms of dominance, as two dominant persons may experience conflicts while two submissive individuals may have frustration as neither member take the initiative. 

Perception and actual behavior might not be congruent with each other. There were cases that dominant people perceived their partners to be similarly dominant, yet in the eyes of independent observers, the actual behavior of their partner was submissive, in other words, complementary to them (Dryer1997). Why do people perceive their romantic partners to be similar to them despite evidence to the contrary? The reason remains unclear, pending further research.

सारखेपणा किंवा पूरकतेचे आंतरव्यक्ति आकर्षणावरील परिणाम Effects of similarity on interpersonal attraction
Similarityसारखेपणा
सारखेपणा किंवा पूरकता Similarity or complementarity?
कारणे Causes