Desirable emotions are the “high-arousal” kind, which are basically those that stimulate people physiologically, causing them to feel more alert. These emotions include joy, amusement, happiness, excitement, awe, shock, frustration, and anger. It has been found that messages that provoke these feelings are much more likely to be shared across social networks. If a campaign or idea can trigger high-arousal emotions (even negative ones), then it’s more likely to go viral.