Imagine a dim room with a little mist in the air.
You click on a flashlight.
A glowing path shoots from the bulb to the far wall, straight as a ruler, not wiggly like smoke. A small toy sits in the beam, and a sharp shadow lands exactly behind it on the wall. How did the light get from the bulb to the wall without bending? Why does the shadow sit right behind the toy, as if the light and the toy and the dark patch all line up?
If light could curve around the toy, would that shadow even be there?