It was about four years ago when I, like many of my friends, abandoned Friendster for Facebook. I never thought about why I decided to jump ship — until I saw the The Social Network a few weeks ago.

The film suggests that what made Facebook a far more desirable network than MySpace and Friendster, the pioneers in social networking, was exclusivity, created by restricting membership initially to students from Harvard and other Ivy League colleges. While the association with prestigious colleges no doubt helped Facebook drive initial adoption and penetrate foothold markets, it doesn’t adequately explain why the site continues to be successful after opening its doors to everyone in 2006.

Many bloggers and journalists have been quick to offer alternative explanations. A cleaner interface, a wider range of apps, and a less juvenile crowd are among the most commonly cited reasons for Facebook’s victory over its predecessors. These are all certainly appealing features, but they are in essence incremental improvements, not the kind of game-changers that could have enabled Facebook to disrupt the social-networking space. To ascend so rapidly, Facebook must be helping consumers to fulfil a key “job-to-be-done”—what we at Innosight call a fundamental unmet need or problem that needs to be solved—more effectively than competing social networks. So what jobs do consumers want to get done on those social-networking sites?

According to a survey conducted by Anderson Analytics in 2009, two-thirds of social networkers would only connect to people they already know in person. Just one in 10 would befriend those outside their existing network. Another study conducted by Pew Internet came up with similar findings. What this indicates is that, when it comes to social networking, “staying connected with people I know” is a much more prevalent job-to-be-done than meeting new people. MySpace and Friendster are targeted primarily at the jobs of “meeting new people” and “expressing myself.” Even though Facebook was a relative latecomer, it was the first social network to focus every aspect of its site on this job.

What made Facebook a superior solution for staying connected with existing friends is its emphasis on control and privacy over accessibility. Facebook gives users control over whom they share information with and who can contact them, essentially enabling users to create their own “exclusive” club and decide who’s in and who’s out. Gate-crashing is discouraged and authenticity is enforced through features like “report spam” and “report/block this person.” This emphasis on privacy helped cultivate a set of norms and etiquettes that reinforced Facebook’s credibility as a network for real friends and connections, even when Facebook subsequently changed strategy and started encouraging more sharing of private information.

To fulfil the consumer job of “meeting new people,” Friendster and MySpace, in contrast, opted to emphasize accessibility. Both sites require users to report their age, gender, and location (and for Friendster, relationship status as well). This information used to be available to anyone, which is a great feature for those who want to find new friends, dates, or scam targets, but a huge annoyance to users like me who are interested in connecting only with people they know. To fend off unwelcomed advances, many users, particularly young females, would grossly inflate their age and report fake relationship status in their profile. Once authenticity was compromised and profiles were no longer genuine, Friendster and MySpace lost the value proposition of helping people meet new people. Later, around the time when Facebook gained popularity in 2006, MySpace and Friendster introduced the option for users to make their profiles private. This was possibly a move to compete with Facebook, but it was too little too late.

I suspect that the reason MySpace still manages to maintain a sizable user base is because it is more successfully addressing the consumer job “expressing myself” than Facebook. By allowing extensive customization of personal profile pages, MySpace enables users to assert their individuality as loudly as they please, while their Facebook profile page would have to look exactly like everyone else’s. MySpace’s growing popularity among bands and other creative industries reflects the site’s success in occupying a niche that Facebook has missed.

Overall, it is fair to say that Facebook has won the biggest battle of the social networks by satisfying the most important and prevalent consumer job-to-be-done in social networking – “staying connected with people I know.” However, there are more battles to be won, and Facebook is fully aware of this, judging from its recent moves in making default privacy settings less private and introducing new features like Facebook Groups and Likes. Let’s hope that, as Facebook forays into new areas of growth, it won’t alienate its core supporters who have no interest in befriending strangers, corporations, or fake celebrity profiles.

Jenny Chung is a senior associate at Innosight.