@Shivviness Gonna say that "intelligence" is a highly problematic construct in this context. That said, in #RentierSociety—where one's autobiographical history of choices made underwrites #EgoValue—educational achievement (oft conflated with intelligence) does tend to be correlated with certainty.
Introspection, OTOH, is arguably near synonymous with doubt, in that introspection entails not taking one's own phenomenology as given. Very act of self-examination begins with questions, not answers.