It is suggested not to look at the sun directly during eclipse. Because ____________________.
Solar eclipses are dangerous because the sun can come out from behind the moon and surprise you before you have a chance to look away. And this is actually even worse than when you normally look away from the sun because during the total eclipse, it is dark out, and your pupil therefore dialates so that it can let in enough light to get a good picture. Then, when the sun reappears and starts flooding the area with really bright light, not only are you staring straight at it, but your eye is in a state where it is wide open, and actively trying to let in as much light as possible.
This explains why it is easy to damage your eye when watching a total solar eclipse, and why you should either be sure to time it very carefully or just view the thing through one of those sets of cheap dark glasses they sell for the express purpose of looking at the sun without getting hurt.