Humans and the Fae
Humans fear the Fae. The word “Faerie” and “fae” are derivatives of Middle English words meaning Fate or “Fated to Die”. For most humans the Fae are not happy pixies, but are mean and scary ogres and goblins. It is true that many cultures have legends of those fae who are helpful and kind, but equally are those that are vicious and cruel. But most are both and will switch to the other at the drop of a hat if you are unfortunate or cunning enough to do so.
Folklore and legends are filled with stories about how to appease them, or ward them away. Learning the name of a Fae and saying its name backwards, making a circle of salt, wearing beads of a specific color. Many fae hold codes of hospitality in high regard and therefore won't attack someone who keeps a clean house (IE is holding a broom), many must obey if you ask them nicely to leave, or may not enter a room unless invited to do so. Many household sprites must pick up thrown food (as a good guest wouldn't allow it) or mop up spills, or check themselves in a mirror. Other fae who see themselves as muses will be compelled to join a dance or song. On occasion more traditional wards like wearing ones' tunic inside out can occasionally work. More recently many fae have recognized the wrath of the church who confuses them for demons and so many have learned the harsh lesson to leave anyone wearing a cross alone.
It is generally known that most fae can be reasoned with if they are not harmed first, making an agreement with a fae has many pros and cons. Many people leave out bowls of cream or horseshoes over their doors as a symbol of this agreement, and as long as the promise is maintained by both parties, it is pretty solid. But if you have no former agreement and you try to leave out a bowl of cream your attempts will be ignored.
Mortals believe in the existence of the Fae, there are reports about them in many cultures. The Fae have no veil yet humans generally do not talk about it out of fear and superstition.