Your observation about how the story will intrude on your everyday life is right on the money. Also, I use that phenomenon as kind of an indicator that I'm "in the zone" with a story--that I've gone into it, some might say.
Until those instrusions start to happen, I'm still in the amorphous "idea" phase, where I'm feeling things out. But once songs on the radio start to remind me of scenes, I think about second-act problems while in line at the bank and I have to catch myself from describing the plot to my wife as I pass the mashed potatoes at dinner, I know the story has finally gotten a life of its own and I'm discovering it as much as I'm creating it.

If you haven't finished that first spec -- discouraged and ready to pitch your laptop out the window -- God forbid chained to it --

STOP!

Close the window... slowly step back... quickly grab a cocktail...

Then print Scott's post.

Let the fresh ink soak through your pores -- place it under your pillow if you must -- do whatever you have to do.

Then get off your butt... place it in front of that cursed laptop and finish your damn story.

Pound it out. The story will find you.

As simple as that.

If you run and you allow "what if..." to take over. More than likely there will never be a second spec and one day you're grey and "seasoned" self will knock on that brain of yours and ask...

"What if?"