What makes online content viral?

I recently read a research paper that attempted to answer this question. I thought it would be useful to summarize some of the key findings. The conclusions were based on the content sharing patterns of NYTimes.

This is a myth — Negative news spreads faster and gathers more eyeballs. The results in this study conclusively show that positive news is actually more viral. Further, by examining the full corpus of New York Times content, the paper concluded that positive content is more likely to be highly shared even controlling for how frequently it occurs.

Another finding -”People said they would be more likely to share an advertisement when it evoked more amusement and a customer service experience when it evoked more anger.”

In the domain of advertisements, humor works better. In the domain of customer service, everyone wants to join in to bash the big bad company. My learning here is that even established companies must actively seek genuine testimonials, and write about the new processes they follow and the good outcomes they deliver. This content will rescue brand managers when something bad happens and users are looking for evidence against the company.

Another finding — don’t post stuff that makes people sad. Even if something is negative, it should be high-arousal and activating in nature such as anger or anxiety. Online content that evoked more of a deactivating emotion (i.e.sadness) is less likely to be viral.
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Unfinished Thoughts: Does virality correlate with conversion and/or recall? What makes people buy — content that amuses or that which addresses concerns such as safety and health?