How do optical illusions prove that you cannot always believe it?

Optical illusions demonstrate that our perception can be easily manipulated, leading us to see things that aren't there or misinterpret visual information. They highlight the gap between reality and our interpretation of it, showing that our brains can be tricked by contextual cues, colors, and shapes. This serves as a reminder that our senses, while generally reliable, can be deceived, teaching us to question our assumptions about what we perceive. Thus, optical illusions illustrate that seeing is not always believing.