Really interesting essay on the nature of growing a startup. What's staggering is how much of a difference a single percent can make. A startup that grows at 5% a week from a base of 50 users will, after two years, have 8,000. 6% will take you to 20k and 10% will take you to a million.

Key point is that focusing on growth—which is the key metric of any startup—turns it into an optimisation problem, which all decisions can then be based upon. If you're not growing, you're a side project, not a startup.

You can use the need for growth as a form of evolutionary pressure. If you start out with some initial plan and modify it as necessary to keep hitting, say, 10% weekly growth, you may end up with a quite different company than you meant to start. But anything that grows consistently at 10% a week is almost certainly a better idea than you started with.

Focusing on hitting a growth rate reduces the otherwise bewilderingly multifarious problem of starting a startup to a single problem. You can use that target growth rate to make all your decisions for you; anything that gets you the growth you need is ipso facto right.

Of course, focusing on the wrong metric can be devastating. User signups are a vanity metric, so you should never focus on raw numbers. But engaged users or paying customers—that's a great metric to focus on.

All PG's essays are great, but this one is amongst the best.