Drew Coffman shares a mindbending optical illusion:
In the video, a distorted window frame appears to oscillate back and forth, even though it's turning in circles. When a pen is inserted through the middle of it, the object does appear to rotate, but that causes you to perceive the pen passing through the center of the window.
We tend to act as if our perception of the world is the objective truth. But the reality is that we are merely piecing together predictions of our environment based on a range of stimuli.
Truth is subjective. And other people's experiences are completely valid even though they may be in direct opposition to ours.
We can understand that fact on a conceptual level, but illusions like this humble us by throwing it into sharp relief.
They remind us that we are flawed, which in turn keeps our mind open.