Complementarity is considered to be cornerstone of Armenia's foreign policy, which was formed during the years of its independence. This approach implies promotion of foreign policy interests of Armenian state, while balancing between regional and world centers of power. Like many other small countries, Armenia had to maneuver between interests of larger players, trying to balance between common interests and topical priorities. In fact, it's a very pragmatic approach, which gives Yerevan opportunity to promote its own foreign policy agenda in turbulent world politics.
According to political analyst Sergey Minasyan, "the most effective manifestation of complementarity in Armenian foreign policy were first two years of independence - 1991 and 1992 - when Armenia was able to use unique foreign policy conjuncture during the Karabakh war, when Yerevan received weapons and military equipment from the Russians, money for construction of statehood (and for purchase of weapons from Russia) from Americans, food and humanitarian aid for population from Europeans, and fuel for its army fighting against Azerbaijan from Iran. This foreign policy was at its peak during the first term of Levon Ter-Petrosyan, which should be considered the most evident stage of Armenia's "complementarity" foreign policy, although it was called that later by ex-Foreign Minister Vartan Oskanyan.
Over the past two decades, Armenia's foreign policy has slowly but surely became completely different. The fact is that international and regional realities regularly changed practical implementation of such foreign policy. For example, closure of Armenian-Turkish border in March of 1993 after Armenian troops occupied Kalbajar blocked any initiatives in Turkish direction. As you know, the attempt to improve relationship with Ankara in 2009 wasn't successful. Final failure of Armenian-Turkish protocols happened over the last months of Serzh Sargsyan's presidency, when he officially annulled them.