Why Can't You Look at the Sun During a Solar Eclipse?

Looking at the sun during an eclipse is more dangerous than looking at full sun. The darkness that accompanies an eclipse can override the natural tendency to squint and avert the eyes, increasing the amount of ultraviolet radiation landing on the retina and making it more likely that you'll sustain eye damage. Your eyes can sustain damage even if only a small sliver of the sun is visible. The cornea focuses sunlight on the retina and scorches it, and because the retina has no pain receptors, you don't know the damage has been done until it's too late.