It is difficult to be aware of whether one knows or not.
[Aristotle, Posterior Analytics I.9 (around 76a26)]
Examples are hardly necessary. And yet we all tend to be tremendously confident about the accuracy of our opinions, and tremendously reluctant to admit our errors when proven wrong. This pride and obstinacy prevents us from learning many things, and it leads us into many needless mistakes. Substituting humility for that overconfidence is difficult…for me, anyway. But the value of admitting the difficulties associated with acquiring knowledge ought to serve as a reminder to us to be intellectually modest.