The Oculus quest, "Old Man Nosek". The start of the quest is obscure. Then, assuming you manage to start it, you are sent to find a person, a chief....spy so to speak. When you eventually manage to find him (this is an open world game, right?), he promptly blows your mind. Anyway, THIS person sends you to find another person, an old hiding scientist, in order to get information on some old scientific project. Intriguing!
But you can't find him. You ask around, you have got your informants as well, and you get some clues of where and who the hiding scientist might be, but clues are not always to be trusted in this game. At any rate, you try to follow the clues, you end up trying to enter a mansion, but you are denied admission.
There are various challenging ways to enter the mansion (and keep in mind you are not even sure he is in there), but the way I first did it is that I quit the quest in frustration and I forgot about it. Later, as 2 other completely separate quests progressed, new NPCs became available. If you happen to talk to them, they give you new ways to enter the mansion.
So you enter the mansion, and you still can't find him, although you get further clues he might be there in the attic. By this point you have access to spying resources, so you put them to use. You EVENTUALLY manage to get in the attic, and an old man is there, and he won't talk to you!
At this point I was throwing breakable things on the wall in frustration. I quit the quest again and went about other business. Then as some other completely separate quest progressed, I got a code to hack a computer in some lab where the scientist used to work. So I hack that computer and get new info. I revisit the old man in the mansion. NOW he will speak!