For today its all about intuition. For me, when I start a project I just know if its really 'the' project or not. Some projects are like little pieces of entertainment and some are the real deal. For me it is all about how I feel about the project. Though I am quite a newbie to writing (I have been writing for probably a year) I do have experience and have started countless projects but I do follow my intuition when it comes to loving a project. Though I don't think I can write as awesome a novel as my debut I have tried out countless ideas from romance to horror and realized that my genre is always fantasy. (Don't question that panther, lol)
Its that feeling you get when you start a project and you just know that you will have to finish it. Because you just can't not follow your character's journeys and you have to end it for their and your own curiosities sake. It doesn't happen for all the projects I work on. So what about you, how do you know when a project is 'the' project?