the rules of writing

So, my first question of the day:

Is learning the rules of writing a good thing or a bad thing?

I ask this because I think of the many writers who write their best book first, before they learn the rules of writing and the rules of the publishing world. Not all writers are this way. Some writers keep writing great stuff, or they reinvent themselves periodically (I think Lois McMaster Bujold has done this successfully, and Robin Hobb, to name a couple). But many, many writers start really well...