The second part is important too: when someone escapes the cave and sees the outside world for the first time, it's painful because things are so bright. After a while, the escapee's eyes adjust, and they come to see how much better and more real the outside world is. They decide to go back and free their friends in the cave. But when they descend back down, their friends make fun of them because they can't see very well in the dark anymore and so aren't very good at talking about the shadows. Their friends think that they are just making up a big story about some magical "outside world" to cover for how bad they've gotten at talking about the shadows.