We all remember being afraid of monsters under the bed. We never saw them. But we imagined what they might look like. Eventually we grew up and the monsters lost their terrifying grip on us.
Same with doubt. From our earliest years we were taught about the terrible monster “Doubt”. And Doubting Thomas was used as the illustration. But as we grow up we learn that doubt is an important ingredient in wisdom. It actually helps us to question That-Which-Must-Not-Be-Questioned in order to move into deeper intellectual territory.