This question pops up regularly on Hacker News. What will kill Facebook? Before that, it was "What will kill Google?" There was no Hacker News before that, but if there had been, it would have been "What will kill Microsoft?"
Often, the question is asked with a combination of rage and envy. The questioner doesn't like Facebook, they want it dead, and they wouldn't mind if they were the one who came up with something that killed it. Aren't entrepreneurs charming?
However, the question is fundamentally flawed. It's the wrong question. It leads nowhere. The only company that can kill Facebook is Facebook. Here's why.
First of all, let's assume that right this minute there is a startup which is just like Facebook 5 years ago. Let's call it Smashbook. Let's further assume that Smashbook is going to do to Facebook what Facebook did to MySpace. We don't know how it might do that, and we don't care. We just care that this is the Facebook Killer.
Take a look at the top 100 sites. What do you find at position 51? MySpace. Wait a minute, didn't MySpace get "killed" by Facebook? They sure did, and Smashbook will have exactly the same effect on Facebook. It will drop from position 2 to position 10. Maybe. After a few years.
In other words, even if a Facebook killer was out today and ripped Facebook a new one, it would still take many years for this to be noticed by Facebook, and it would take decades before it finally did kill Facebook.
Ok, but how to kill it?
Is it even possible for Smashbook to exist? The evidence of Facebook killing MySpace would point to 'yes', but this is not so clear. When Facebook came on the scene, MySpace already had many issues. Due to MySpace's design and its demographic, large groups of people were simply not interested in joining MySpace, and so MySpace already carried the baggage that would eventually cause it to get trampled by Facebook.
Facebook, on the other hand, doesn't have any such flaws. You might say that privacy is Facebook's flaw - Diaspora and others are certainly betting on that - but, unlike design and demographics, privacy is not something that most people care about. The odd geek will get angry and leave Facebook, but for most, privacy is of no interest.
In this, Facebook is similar to Google: it has utterly dominated its market and has such a lead over its potential competitors that no one can catch it. Facebook is as unkillable as Google.
So how unkillable is Google?
To see whether Google can be killed, let's look at the previous "unsinkable" title-holder: Microsoft.
Microsoft is far from dead (and probably will never die), but it has made a very good attempt on its own life in the last decade. With Windows Vista, Microsoft did what it could do commit suicide on its flagship product. Six years of delays, bugs, driver support issues, usability issues, and so on - Vista had them all. And yet even that didn't work. Microsoft's revenues barely took a hit. Like any company of this size, it will take decades for it to kill itself, and it will have countless chances to avoid death along the way (and probably will successfully take one of them).
No company is really "killing" Microsoft. What may be killing Microsoft is its own failure to adapt and evolve with the times. What will eventually kill Microsoft's current cash cow is the slow but inescapable disappearance of the Windows/Office monopoly, to be replaced by "the cloud", whatever form it eventually takes.
Google, similarly, will be killed not by a competitor rising out of nowhere, but by falling into irrelevance. This will take many, many years, and Google will have many chances to jump onto whatever the next wave of relevance is.
So, back to the beginning.
What will kill Facebook?
As I said at the beginning, this question is flawed. Facebook, like Google and Microsoft before it, has risen on a giant wave, that of social networks. As an entrepreneur, thinking about "killing Facebook" is unproductive. You won't kill Facebook. No one will.
The right question to ask, instead, is:
What will be the next giant wave?
If you can figure that out, and execute the right business to catch that wave, and beat every other business who sees it too, and end up king of the hill at the top of the next wave, then you will have beaten Facebook in the only way which is meaningfully possible. Chances are, when you get there, you won't care much about how to kill Facebook, or any other mega-company.
If you read this far, you should follow me on twitter here.