St. Louis's Gateway Arch is one of the world's largest optical illusions. It appears to be much taller than it is wide. The reality is that it is as high as it is wide. The problem is that the illusion can't be overcome just by taking another look — only an objective measurement will do.
The relationship to unlearning is this: You can't simply rely on what you see to be the sole determinent of truth. In many cases only objective measurement will do.
For example, as I explained in this video, people often "see" patterns when none exist. Alternatively, we tend to view people based more on their surroundings and environment than on who they truly are.