Social media generates a prodigious wealth of real-time content at an incessant rate. From all the content that people create and share, only a few topics manage to attract enough attention to rise to the top and become temporal trends which are displayed to users.The question of what factors cause the formation and persistence of trends is an important one that has not been answered yet. In this paper, we conduct an intensive study of trending topics on Twitter and provide a theoretical basis for the formation, persistence and decay of trends. We find that the resonance of the content with the users of the social network plays a major role in causing trends. Also, we observe that a majority of the content propagated to cause trends arise from traditional media sources with social media acting as a selective amplifier for them.