I started playing a game, "The Talos Principle" yesterday. It's a puzzle game with philosophical/religious overtones. Throughout the game you find little snippets of communication from in-game people or passages from books (real-life and in-game). I thought this section of an in-game speech was particularly on point and relevant to my recent ruminations:
They say "doubt everything," but I disagree. Doubt is useful in small amounts, but too much of it leads to apathy and confusion. No, don't doubt everything. QUESTION everything. That's the real trick. Doubt is just a lack of certainty. If you doubt everything, you'll doubt evolution, science, faith, morality, even reality itself - and you'll end up with nothing, because doubt doesn't give anything back. But questions have answers, you see. If you question everything, you'll find that a lot of what we believe is untrue...but you might also discover that some things ARE true. You might discover what your own beliefs are. And then you'll question them again, and again, eliminating flaws, discovering lies, until you get as close to the truth as you can.
Questioning is a lifelong process. That's precisely what makes it so unlike doubt. Questioning engages with reality, interrogating all it sees. Questioning leads to a constant assault on the intellectual status quo, where doubt is far more likely to lead to resigned acceptance. After all, when the possibility of truth is doubtful (excuse the pun), why not simply play along with the most convenient lie?
Questioning is progress, but doubt is stagnation.