You have probably seen a number of virtual illusions that prove the limits of our perception (and “perfection”!), such as the one below, or the one where you are asked to compare the length of two lines. Easy stuff, right?
Well, why don’t you try this fun interactive Online Experiment, on the Muller-Lyer Illusion. It takes a minute. You will see your results, and an explanation, once you complete the task.
Link to a neuropsychological explanation.