Faeries are probably not immortal- they can succumb to fatal attacks, for example, and have a very long, but not infinite life span, at the end of which they will expire from exhaustion and debility, like any human- but their ability to survive for hundreds (if not thousands) of years inevitably shapes their interactions with us mortals and, arguably, their own mental states.
I have discussed previously how faery vengeance may be postponed over centuries, so that some human misdeed is punished long after the perpetrators have died and their descendants have forgotten the offence and the consequent threat hanging over them. This is best represented in the Welsh case concerning a farmer at Pantannas; to mortal readers it seems incredibly unjust that later generations, wholly innocent of a forebear’s sins, should be punished but, in defence of the faeries, we have to appreciate that the delay in taking revenge will, to them, have seemed only the matter of a few weeks or months (in human terms).
Other implications for humans include the disastrous effects of spending time with the faes in their homes. What may to the human visitor may appear to have been only hours or days will turn out to have been decades (or more) on the earth surface. The joy of return to loved ones is instantly destroyed because all the returnee’s family and friends have long ago died and, in the worst cases, even the landscape has transformed: homes have fallen into ruin; woods have been felled and fields changed. Wirt Sykes gives several such stories from Wales in his British Goblins. Give a thought as well to those humans with faery lovers: the human ages yet the supernatural partner stays ever young. These are not equal or sustainable relationships and they can only be made to work by sacrifice by one party or the other; someone has to abandon their home and kin to stay with the beloved. Many will immediately think of Tolkien’s Arwen and Aragorn, which dramatises this ancient dilemma very well.
In this last example, there is pain, too, for the faery. Another example of such suffering, in a rather different context, can be found in the story of the Cauld Lad of Hilton. This being appears as a sort of hybrid creature- partly brownie, but partly ghost as well. The liminal nature of many faery beings (especially in the north of Britain) is common- there is frequent uncertainty over whether boggarts, brownies and others may best be classified as sprite or haunting spirit, and in the case of the Cauld Lad he was reported to be a stable boy cruelly beaten to death by a Lord of Hilton. He worked in the kitchens at night, and could be heard to sing a sad song that bewailed his trapped state:
“Wae’s me, wae’s me,
The acorn’s not yet fallen from the tree,
That’s to grow the wood,
That’s to make the cradle,
That’s to rock the bairn,
That’s to grow to the man
That’s to lay me!”
He wanted to escape his ambiguous status, neither fully alive nor dead, and- luckily- the servants of the house took pity upon his lonely plight and decided to give him a cloak and hood to cover his naked, cold form and, thereby, laid or exorcised him (just as happens so frequently with brownies and boggarts).
What’s notable about his song is not so much that the Cauld Lad was wrong about how long he’d have to wait to be released, but the terms in which he measured time. We seem here (once again) to be dealing in centuries, from the sprouting of the new tree to its felling and the use of its timber; for some readers the formula used here may be familiar because almost identical words are often used by changelings when they are being exposed as faeries by their human hosts. Most typically the trick of cooking or brewing in eggshells is played upon them, and the apparent human infant will exclaim something along the lines that “I have seen the first acorn before the oak, but I have never seen brewing done in eggshells before”- in other words, they have already lived for many centuries and are plainly faeries, not babies or toddlers as they outwardly appear.
The disparity between faery and human perceptions of time inevitably place a considerable and often unbridgeable gulf between us and must always be factored into our assessments of their behaviour and motives. For more detail of some of these subjects, see my British Brownies and Faery Lifecycle.