I really liked this post from Dharmesh – Failure Is Not The Worst Outcome, Mediocrity Is, especially this para.
How do you know whether you’re stuck in a quagmire? Isn’t startup success often about persistence and focus? What if that break-out success is just around the corner. Those are good questions. The simple answer is: There are no simple answers. If it were me, the question I would ponder is this: If 90% of everything started going “right” with your startup, what will it become? (I’ll call this the “wave the magic wand”, best-case scenario). If the answer does not please you, and you’ve been at your current idea for a while, I’d ponder a change.