  Understanding social interactions and generous behaviors have long been of
considerable interest in the social science community. While the contagion of
generosity is documented in the real world, less is known about such phenomenon
in virtual worlds and whether it has an actionable impact on user behavior and
retention. In this work, we analyze social dynamics in the virtual world of the
popular massively multiplayer online role-playing game (MMORPG) Sky: Children
of Light. We develop a framework to reveal the patterns of generosity in such
social environments and provide empirical evidence of social contagion and
contagious generosity. Players become more engaged in the game after playing
with others and especially with friends. We also find that players who
experience generosity first-hand or even observe other players conduct generous
acts become more generous themselves in the future. Additionally, we show that
both receiving and observing generosity lead to higher future engagement in the
game. Since Sky resembles the real world from a social play aspect, the
implications of our findings also go beyond this virtual world.
