Intelligence is not thinking you know everything without questioning, but questioning everything you think you know.
This is not the same as skepticism. It is not questioning that knowledge is possible, it is question whether I have knowledge. As Descartes wrote in his Meditations, what we need to keep in mind is “I could be mistaken.” A rule for the mind, he said, was to never precipitously accept anything is true but to patiently question everything that we think is true. This is true intelligence.