There’s something very special in folklore stories from storytelling point of view. I mean, stories that have an author are made by one person and reflect his or her personal worldview and imagination. Folklore stories on the other hand are polished by generations. They are not written so some details get forgotten and some others get amplified. The story varies a bit each time it’s told and every person involved has a small role in shaping it. So wouldn’t it be proper to say that folklore stories reflect on some common wisdom?
Depending on the country, themes of folklore change too. Sometimes it tells about danger of romantic love, other times about pure survival under unfortunate circumstances, and sometimes we have the whole mythology — the creation of the world, gods, spirits…
Another feature of folklore is rituals. Most of northern countries have a fest in the beginning of spring to defy winter or to welcome summer. There are rituals for young girls to find their soul mates (like Ivana Kupala) and something you do when somebody dies to help the soul travel with less hardship.
Many folklore stories are dark. I think the reason is, they suppose to serve as a guidance for one in trouble (like The Wild Swans) or help one not to get in trouble (so many stories starts with children who went into a forest). So showing the darkness folklore isn’t build to upset people of say that the darkness is all there is, but to give people hope and intuition and advice about going through major life change. Did this advice get outdated because modern society changed so profoundly? On some level yes, on the other things never change.