Take a look at the picture below. Do you see spirals of green and blue colors embedded in pink and orange stripes? Would you believe me if I said that the green and blue are actually the same colors? Yes, they are identical!
This blog post (by Phil Plait) on the Discovery Magazine explains the reason why this (optical illusion) happens. It has to do with the way the brain judges the color of an object — by comparing it to the surrounding colors.
The upshot is that our eyes and our brains can be easily fooled. As Phil Plait writes:
This is why I tell people over and over again: you cannot trust what you see even with your own eyes. Your eyes are not cameras faithfully taking pictures of absolute truth of all that surrounds you. They have filters, and your brain has to interpret the jangled mess it gets fed. Colors are not what they appear, shapes are not what they appear [...], objects are not what they appear.
So the next time someone swears they saw Jesus, or a UFO, or a ghost, show them this picture. What you see in life is absolutely and provably not what you get.
The cognitive illusions are not limited to visual perceptions. In a brilliant TED talk (see below), behavioral economist Dan Ariely shows how our behavior and our decisions are sometimes driven by things that seem completely irrelevant — how our seemingly rational behavior can be perfectly irrational. Quite shocking and insightful, this lecture.
Here’s an earlier related post: Cognitive Biases and Nudge.
