One possible moral could be that we should face our fears instead of avoiding them. In the story, the characters often have to deal with the monster under the bridge, which represents a fear. By confronting it, they might grow or learn something valuable.
There's the monster, of course. It's the main source of conflict in the story. It could be a big, hairy, and scary - looking creature with sharp teeth and claws. And then there are often villagers or townspeople who might be aware of the monster and warn the travelers about it.
The location under the bridge could be a place of isolation. It might signify that the girl is in a marginalized situation, away from the normal hustle and bustle of society.
I'm not sure which specific 'under the bridge' story you are referring to. There could be many stories related to something under a bridge. It could be a local legend about a hidden treasure under a bridge, or a story about a person's experience living under a bridge.
The song 'Under the Bridge' by Red Hot Chili Peppers was inspired by Anthony Kiedis' real - life experiences. He was struggling with drug addiction at the time. The 'under the bridge' referred to a place in Los Angeles where he used to go to get away from his problems and think. It was a very personal and emotional song for him.