Well, some would say that failure is the inescapable final consequence of human existence, but then again those people don't get invited to parties for a reason.
So all intransitive verbs end in s?
But couldn't this take an object like for example "de mislykkes eksamenen" (they failed the exam), or is this verb used in another context that doesn't have to do with failing at something?
I would bet it's actually "eksamenen mislykker...". If it's like German missglücken, then it's the thing they are trying to do that is mislykkende.
I understand why other verbs are, but why is this verb mislykkeS and not mislykkeR? I thought the s ending was mainly used for things people do together
from what I have read here in the comments, it seems the final -s comes in place of -r where there can be a "hverandre" (each other) implicit. So here the meaning might be "why are they failing each other?". You can also choose to use the -r termination AND the "hverandre".
Why the -s? If I use the previously mentioned examples we will get they rest - de hviler, they sleep - de sover. My feeling is that the difference is: failing was something that just happened to them and not something they chose, like with the other two verbs. I don't really know, though.