The Maverick Philosopher has a post here where he asserts that doubt is the engine of inquiry. But surely more fundamental to inquiry, as Aristotle says, is wonder. For you can doubt something without any urge to find out the real truth. In fact, that seems to sum up the ignorant cynicism that passes for sophistication these day.
The oracle at Delphi told Socrates that he was the wisest of men. This puzzled him because he knew he possessed no special knowledge. Did Socrates, then, doubt the oracle? Perhaps, but more significantly, he set out to find someone wiser than himself and prove the oracle wrong. The motivation for this was not doubt, but an urge to see the truth vindicated. If Socrates had merely doubted, he would have heard the oracle, not believed it, and just gone home.