Optical illusions are fun because you literally can't believe your eyes. But isn't it a little troubling that your eyes can get fooled like that? Why don't they show you the visual truth? How can you ever trust them if they don't?
Well that's not their job. You can't handle the truth. As ASAP Science explains, your peepers have painstakingly evolved to show you what you need to know in a way you can understand it. If you saw everything, you'd drown in the noise. Optical illusions are just a window into exactly how your eyes and brain team up to try and show you the world in context, in a way that makes immediate sense.
So don't worry; if you needed to see the truth behind optical illusions, you'd be dead by now.