The myth is pretty easy to dispel when the Maker himself has admitted to it. Here’s an excerpt from a letter GL wrote to the showrunners on LOST:
Congratulations on pulling off an amazing show. Don’t tell anyone … but when ‘Star Wars’ first came out, I didn’t know where it was going either. The trick is to pretend you’ve planned the whole thing out in advance. Throw in some father issues and references to other stories — let’s call them homages — and you’ve got a series.