This morning I thought I'd do some digging to try and find what people think about why Facebook became so successful. Most answers that I found didn't really capture what I thought about the issue (not even Zuckerberg's own opinion), so I decided to give a bit of an alternative perspective on it.
As Malcolm Gladwell pointed out in Outliers, someone's success is not independent of their history. For example, Bill Gates had already built up over 10,000 hours' experience by the time the opportunity to start Microsoft came along, and there are probably a number of examples of people who had similar experience to Gates but were just "one year too early or late". Success is obviously a combination of both hard work and opportunity.
Now that that's out of the way, let me state why I think Facebook's strategy was so successful - I'll get to why Google+ wasn't. The closest answer to mine that I could find was this one on Quora (see point 1 of Todd Perry's answer relating to "attacking hubs"). Yes, Zuckerberg had the right amount of technical expertise, but that isn't the chief reason why their strategy was successful - many people have similar or even greater levels of technical expertise, but haven't started Facebook. Yes, the owners have been aggressive about growing the site - show me someone who isn't aggressive about growing their business. Yes, Facebook appeals to a side of ourselves that struggled to find expression prior to the existence of social media - MySpace, Friendster and countless others (including Google+) all do similar things, yet where are they today, really, in comparison to Facebook?
The answer, in my opinion, can be best articulated using terminology from Lila, the sequel to the classic Zen and the Art of Motorcycle Maintenance by Robert Pirsig, as well as an understanding of social influence (power). This is a bit philosophical (abstract) at points, but I guarantee you it's worth understanding if you're in business.
In Lila, Pirsig divides reality into four "levels" of patterning: inorganic, biological, social and intellectual. Biological patterning (such as cells) cannot exist without inorganic patterning (the molecules that make up those cells). Social patterning (immediate, pre-intellectual gestures and responses between biological organisms, and social influence/power) cannot exist without biological patterning. Intellectual patterning cannot exist without social patterning (for a discussion of how we think mind emerges only from social interaction, see this article).
One thing we've been missing out on in our understanding of business is a thorough understanding of power and its role in society, and my opinion is that Facebook inherently managed to leverage the right amount of social influence at the right times to slingshot them to success.
How exactly did they do it? It was both easy and difficult (easy for Zuckerberg, difficult for the rest of us). Think about it: the first institution whose members were up on Facebook was Harvard - one of the most powerful, influential institutions in the world, with their students being incredibly influential people in society. Several other influential institutions followed, and before they knew it, everybody who was anybody was on Facebook. It was only a matter of time before the nobodies (such as myself) were on Facebook. (By the way, I've since deactivated my account, for a variety of reasons).
According to this perspective, therefore, I (being a nobody) should not have received an invite to the Google+ Beta version, but I did! Who the heck am I in the bigger scheme of things? Apart from being a few years too late to jump onto the social bandwagon, this was Google+' single biggest failing. Their entry strategy was flawed from the beginning. According to this article, Facebook has around 850 million users at the moment - Google+ has around 10% of that (90 million - and even that might be an optimistic estimate). (And no, I'm not on Google+ either, for a variety of reasons).
I am not at all discounting the value of incredible technical skill - it's an essential component to getting your business up and running, and is mission- critical for high-tech businesses. You simply cannot afford, as a small start- up, to have your site/application fall over just when people start liking it, because then, just as quickly, they stop liking it. Also, I am not at all discounting the value of getting the right amount of start-up capital, if you can't bootstrap your business, at the right time, or addressing the real customer need/desire, or having the right people, etc. Facebook certainly got a lot of those things right too.
What I am saying is that a successful strategy seems to be one that also takes into account social influence. Start off by convincing the right users - those with the most social influence - to use your product/service, and you'll find it'll be much easier to convince everybody else to do the same. That could be an incredibly easy or hard task, depending on how connected you currently are, and Zuckerberg was fortunate enough (this is the "opportunity" component of the opportunity/hard work mix about which Gladwell talks) to have direct access to some of the most influential people in the world to promote Facebook for him.