When Is Doubt Helpful?

Our doubts can range from healthy skepticism to unhealthy paralysis. Everything from questioning someone’s intentions to doubting our faith (or lack of it) can be beneficial or crisis-inducing.

When is doubt helpful? Or, more specifically, how do you know when it’s good to listen to that inner voice of doubt?

Related questions:  What do you do that you shouldn’t? When is it useful to fail? What is necessary to change your mind? How important is intuition?