As we wander through this life, we learn a lot about how things work. We develop strong intuitions for the physics of the world. Sometimes, however, our perceptions lead us astray.

The figure at the right is known as the Lyell-Müller illusion in psychology. Both lines are the same length, but the arrows lead the eye, causing the viewer to interpret the line with the open arrowheads (>–<) as longer.

We use this icon to remind you that you cannot always trust your first intuition and that we often have to check our expectations via measurement. When some of our intuitions mislead us -- or are inconsistent, we may have to think through what experiences they are based on and refine and reconcile our intuitions.