We demonstrate here a simple physical picture of liquid-glass transition, which qualitatively explains most of the dynamic features from the strong-glass to the fragile-glass limit. We classify the dynamic environment of a molecule into loose and tight cages. Glass transition is then characterized by two transitions : (i) the appearance of tight cages at the crossover temperature T-c and (ii) the disappearance of loose cages at the Vogel-Fulcher temperature T-0. We propose that the fragility of glass is strongly correlated with the relative importance of the topological confinement against the anisotropic attractive intermolecular interactions for the formation of right cage.