Marketing and PR pros often wonder why some videos “go viral” and quickly attract thousands or even millions of views and shares while others draw much less attention even if well-produced and heavily promoted.

Stephan Spencer, founder of Science of SEO, examines two YouTube videos to learn why. One video relays the story of Arthur, a disabled Gulf War vet who was told he would never walk without a cane. With yoga and determination, he loses 140 pounds in 10 months and regains full mobility. The video had over 13 million views as of the article’s publication.

The other video tells the story of Derek, a US Marine captain who was paralyzed in the line of duty and learns to walk again with high-tech prosthetics. It has a good premise and is well edited. Yet despite a similar theme, that video had about 6,800 views.

Powerful storytelling. Arthur’s video uses the power of storytelling to create a strong emotional connection. It portrays a problem with complications, challenges and final success. Viewers see him fall but try again. Through strong storytelling, it reaffirms why viewers should continue watching every few seconds. Derek’s video presents a problem and then provides a quick solution.

A strong start and hook.  Derek’s video required about a minute to establish the problem and challenge. Video marketers recommend getting to the main action to grab audience interest within 15 seconds.

Action. Although Arthur’s video has still images, it also has segments filled with movement. Derek’s video is more like a photo montage.

A fulfilling conclusion. Arthur’s video provides a more fulfilling conclusion. “Simply put, I think we aren’t as amazed by this technology as we are with how yoga transformed Arthur,” says video marketing expert Jamie Salvatori, founder of novelty online retailer Vat19.

A strong marketing start. Factors other than video quality and story account for the differences in view numbers. Arthur’s video was initially shown on the YouTube channel of Diamond Dallas Page, a well-known AMA fighter-turned-yogi, who has over 100,000 subscribers. It was also uploaded a couple years before the other video, allowing it more time to acquire views.

Small Brands Can Go Viral

Well-known brands with large marketing teams and agency specialists can produce videos that go viral more easily than small businesses and nonprofits. However, even small companies with meager resources sometimes hit the social media lottery, sometimes unexpectedly.

Meg Prater, content strategist at Brandfolder, analyzes 12 small brands that created viral, or at least highly successful, videos in a HubSpot article. Here are some lessons from a few examples.

Know your audience. Subscription photo service Chatbooks created a video to educate viewers about its new app that turns photos into albums. The video has gained a million views to date and helped sell a million subscriptions in its first 18 months. The video features a busy, realistic mom whom other moms can relate to. Chatbooks clearly thought through what moms worry about, how they spend their time, and how they fit photos into their hectic schedules.

Latch onto another brand’s viral success. Photos of a dress went viral when people couldn’t agree it its color. While dressmaker Roman Originals certainly benefited from the craze, Dunkin’ Donuts, Legos and Tide and other brands capitalized on the dress controversy with clever dress-themed marketing strategies.

Prepare a PR plan for the best and worst. Invisible Children, an activist group dedicated to bringing Uganda war criminal Joseph Kony to justice, gained sudden and unexpected attention with its YouTube video Kony 2012. It wasn’t prepared for the deluge of attention, web traffic or criticism the video caused. Skyrocketing site traffic, a manpower shortage and the lack of a PR agency and PR strategy all contributed to extensive chaos.

“It’s nearly impossible to know what will go viral, and trying for that elusive result will usually come across as forced and futile. Instead, research your target audience, decide if you can expand that audience, and create campaigns that are thoughtful, actionable, and relevant,” Prater advises. “But before you launch, make sure you’re prepared for the maelstrom that could follow.”

Bottom Line: Marketing and PR pros can increase their chances of creating popular videos by examining examples of videos that went viral. Most importantly, a strong story and emotional connection keeps viewers interested and encourages them to share the experience with others. “Happy” videos make the most likely viral winners.