Sander van der Linden for Scientific American, on viral altruism and how most social charity campaigns spread fast but burn out faster: 

In competing for the public's rapidly shifting attention span, mobilizing audiences to large-scale collective action is a daunting task. Viral social campaigns can effectively capture the attention and support of mass audiences, but in order to make viral altruism stick, more gradual and deeper engagement with a social cause is required over a sustained period of time.