The first line of everything is an excuse. Mostly to continue with whatever that first line has started - a text, a talk, a conversation, a music piece, a heroic epic, a lifelong love commitment, a [something]. Whatever it starts, that first line is not it. It's just the declaration that discourse has begun, and that a proper response is in order.
Beowulf starts out with the word "hwat!", which I can just imagine being used to make the very rambunctious contemporary audiences hark and listen. The function is not so much semantic as social - listen up, everyone!
Everything needs that "hwat!". No matter if it's a blog post, a novel, a twitter conversation, a complicated orchestral piece or an international diplomatic conference. That first statement will always serve as an excuse to keep going, no matter what the keeping and going is about.
Which is why "it was a dark and stormy night" is not such a bad way to go about it. It sure beats that feeling of staring at a blank page not knowing where to go - not having an excuse to continue, as it were.
So. It was a dark and stormy night...