This headline, “Exec loses job after allegedly slapping toddler on plane,” is an anger-evoking true story that spread quickly. Understanding why can help you spread your ideas, piggybacking on certain kinds of momentous events. “High arousal” negative emotions such as anger or anxiety spur us to share messages with others, discovered Wharton professor Jonah Berger, author of Contagious.

So do certain high-arousal positive emotions: awe, excitement and amusement or humor. Susan Boyle’s unexpected singing performance, for example, evoked awe and 100 million views within nine days. Even years later, she inked a movie deal. Les Miserables’ movie producer Cameron Mackintosh said her success reinforced his interest in making that movie.

Evoke pride and other high-arousal emotions

Evoking pride or righteous anger also spurs sharing, according to Scaling Up Excellence co-authors and Stanford professors Bob Sutton and Huggy Rao, because “such feelings make people feel powerful and in control of the world around them, which in turn triggers assertive and confident action.”

Evoking pride instead of shame made a success of the anti-littering campaign “Don’t mess with Texas.” To get Stanford soccer players to agree to wear helmets, fellow students littered their field with smashed watermelons and then created and posted photoshopped images around the field of unprotected heads of soccer players next to the watermelons.

Evoking pride or righteous anger also spurs sharing, because “such feelings make people feel powerful and in control of the world around them, which in turn triggers assertive and confident action.”

Warning: Some emotions stifle our desire to share

Not all positive emotions actually motivate us to share ideas with others, Berger discovered. “Low-arousal” positive emotions in response to a message, such as contentment, don’t spur us to share.

Tie your product to familiar and frequent situations

Even citing mutuality between products can help us see yours more often. For example,  ”Kit Kat and coffee break“ can sound like a rather bland brand slogan. Yet sales skyrocketed. Why? Because the company tied its ad campaign to a frequent habit for many people: drinking coffee. Those who see the message, or its offshoots, may be triggered to think about eating a Kit Kat candy bar whenever they take a coffee break.

Conversely, GEICO’s attention-grabbing TV ads suggesting that switching over to their auto insurance was so simple that even a caveman could do it were not as successful. As Contagious author Jonah Berger points out, “We don’t see many cavemen in our daily lives. The advertisement is unlikely to come to mind as often, making it less likely to be talked about.”

Hint: Connect your message to a situation that your kind of customer frequently experiences so it triggers them to think of your product whenever they are in that situation.

Danger: Don’t do this. Translation: But many others are

Some widely visible “anti” campaigns that attempt to stop certain behaviors, such as kids using drugs, instead evoke the opposite reaction because they give the habit more visibility, thus social currency. Public service announcements that warn of such dangers actually serve as “social proof” that many people appear to be doing it, so it must be okay, thus encouraging young people to use marijuana.

Connect your message to a situation that your kind of customer frequently experiences so it triggers them to think of your product whenever they are in that situation.

Focus on real-life exposure to transport your message

Most people believe that at least 50 percent of word-of-mouth messages happen online. “The actual number is 7 percent,” writes Berger, citing Keller Fay Group research. That may be because “it is easier to see,” adds Berger. “Social media sites provide a handy record of all the clips, comments, and other content we share online. But we don’t think as much about all the offline conversation we had over the same time period because we can’t actually see them.”

If you want to lead a purposeful life, swaying others here are two other books to read.