Many people do! This is the 'architect' vs 'gardener' debate. A lot of writers start out with the notion of a story, then let it develop in the writing. If I remember correctly, Stephen King writes this way.

>Does this mean that, for instance, if you're writing a novel, you start without a structured outline?

It could, but there's no reason you couldn't start with a terrible outline instead of diving right into prose. The point is just that when you see something your brain will stark noticing all the ways it sucks and it gets things going.