Two main questions arise when one seeks to explain the propagation of light in a dielectric medium: (i) Why does the wave slow down? (ii) Why is there apparently only a forward wave? There is a subtle answer to these questions provided by the Ewald–Oseen extinction theorem, but the physical mechanism involved is not very easily visualized. This article sets forth a simple one‐dimensional model of parallel polarizable slabs that makes the mechanism clear and links the two questions in an interesting way.