Asking "why?" in general is a good place to start, because there's also:
--Why isn't anyone else doing this? (Depending on your idea, they probably are. Hint: if it's idea A + B = C, they are.)
--Why me? (If you can't answer this, then it shouldn't be you.)
--Why this and not something else? (If you can't muster up some passion, save yourself the time.)
In other words, "why?" is one of the toughest questions to answer, and keep answering because you can always ask "why?" again. But if you CAN answer it, you may just have something.
--Why isn't anyone else doing this? (Depending on your idea, they probably are. Hint: if it's idea A + B = C, they are.)
--Why me? (If you can't answer this, then it shouldn't be you.)
--Why this and not something else? (If you can't muster up some passion, save yourself the time.)
In other words, "why?" is one of the toughest questions to answer, and keep answering because you can always ask "why?" again. But if you CAN answer it, you may just have something.