It is a common theme in many anecdotes and stories for the fairies to fiercely guard their privacy. They are well known to react badly to being spied on in many cases and to expect humans who they favor to keep any gifts and friendship largely a secret. We see this idea played out in stories of borrowed midwives who accidently anoint their own eye with an ointment that grants true sight of fairies only to admit having the ability later and be blinded, as well as in tales of fairy lovers who abandon their human sweetheart when that human tells a single person of their existence. In some stories of those who received money from the fairies, when they spoke too openly about it or bragged they found the money stopped coming to them or even in a few stories that the wealth they had been given was reduced to leaves, gingerbread, or the like. In all but the rarest cases once offended the fairies good favor was withdrawn and contact ceased, despite any effort by the human to regain it. As with the 'thank you' rule this is not an absolute blanket prohibition and we do see exceptions where a person is allowed to speak of them or forgiven for breaking this rule, but when they react badly they react extremely badly, as in the blinding example already given.
As with many of these taboos the exact reason for it is never spelled out explicitly but we can perhaps offer some possibilities. I think to begin we need to break this down into the two issues we are actually dealing with which are related but separate; their dislike of being observed against their will or without their consent, and their dislike of being spoken of by someone who has agreed not to do so. In the first case the real issue is that the Good Neighbours prefer, generally, to move unseen in the human world and when this invisibility is somehow breached by a human it upsets them. There is a clear logic to their reacting badly to being seen when they do not wish to be, since moving unseen is a main way they survive in our world and is one of the many ways they have power here. The second issue, however is as much one of trust as concern over actual privacy as it represent someone telling a secret they have usually been asked not to tell. It is also true in a wider sense that they dislike people who brag overmuch and tend to respond to human arrogance by taking actions to punish the people; in these cases someone who receives a boon from them and then talks too much of it may find their good luck withdrawn simply because they have annoyed the Gentry with their bragging.
Why do the Good People not want everyone to know how active they are in the world or how many people are receiving their blessings? Perhaps because the Fey folk are a people with their own agency and agenda and they prefer to control who knows of them, sees them, and receives good from them.
It is an old belief that if you have the Second Sight and see the Good People when it's clear they don't realize you can see them that you should not in any way acknowledge that you can see them; I suggest this same approach to anyone who thinks they may have seen the fairies unawares. If you are fortunate enough to have gotten a gift from them or if they have done you a kindness and it was a one time thing it is generally safe to talk about it, however if they have a pattern of helping you, or if they have asked you or made you promise not to speak of what was done on your behalf you must not do so. If you are unsure if its alright to talk about a personal experience or something you've seen, my best advice is to err on the side of caution.
|Emhain Macha, 2016, copyright M Daimler|
Yeats, W. (1888) Fairy and Folk Tales of the Irish Peasantry
Lenihan and Green (2004) Meeting the Other Crowd
Briggs, K., (1976) A Dictionary of Fairies
Narvaez, P., (1991) The Good People