Lucas said it himself when he wrote a letter to the producers of Lost:
“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.”
Wow, I had no idea this happened but that’s hysterical. Kind of confirms that he’s been lying about everything for years.