Well, both. Inspiration is what creates the spark of an idea in the first place. Inspiration is what keeps you interested in that idea, as characters, plot points and emotional climaxes occur to you one by one throughout the writing process. Inspiration keeps you afloat as you face draft fifteen of the first episode, or yet another notes meeting with a totally different group of execs to the ones you met last time, all of whom have contradictory ideas.
But inspiration is like love – you don’t feel it all the time. The wild flush of emotions you feel when you fall in love aren’t supposed to last through a fifty year marriage, and the first flush of inspiration won’t last through the writing of a novel or a screenplay either. But that’s fine. They’re supposed to be replaced by new emotions, a new and evolving relationship with the loved one – or the script.
As long as it is full of self-sacrifice, the initial infatuation will always grow into a stronger, more mature love.