From the Website:
SFX! games are designed to be "Simple, Fast and eXciting!"™
The mission of SFX! is to answer the question: How can I play an RPG set in a genre that actually feels like that genre as it’s being played? By making the Primary Rule "Does this sound like the genre?" trump all the other rules, SFX! ensures that whatever else is happening, the players are never prevented from accomplishing some action perfectly in keeping with the genre just because the rules don't cover it, or forbid it. At the same time, by giving the players specific, concrete rules to resolve whether genre appropriate actions actually succeed in that specific case SFX! makes it possible for the results to surprise everyone at the table, unlike strictly free-form story telling games.