system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't humans see clearly underwater?
gpt
Light travels differently in water, due to the refractive index of water.  That's why looking through the surface of water, straight objects can look bent, and spearfishing is so difficult!  Since we are evolved to see through air, our vision gets screwed up when looking at light through water.  Having an air pocket between the water and the eyeball like in goggles solves this as the light goes back to normal speed in the air.