So your adventuring party is exploring a ruined city that has been inhabited only by monsters and bandits for the last 1,000 years. During the adventure, they stumble upon a secret door that leads them into the laboratory of a long dead alchemist and discover his recipe book. They bring it back to civilization and it winds up revolutionizing the field of alchemy. Normal stuff for adventurers, right?
But does it make any sense? No. The lab has been lost for centuries, but these guys who never spend more than 10 minutes searching any room happen to find the secret door, open it and reveal an intact lab, with valuable loot, that no one else has discovered in 1,000 years. And it isn’t materially damaged. Right!
I did this recently. A party I GM for was searching a ruined giant city. This thing is only a couple of days away from a major city and has been gone over by historians dozens of times. But they found the secret smithy. Granted, no one else was really looking for metal working; they were looking more for treasure or historically significant artifacts. But they found it. Some of the traps no longer worked. Some had been set off by previous treasure seekers. Some they avoided themselves. In the end, they walked out with the Rosetta Stone of smelting - a stone tablet with the formula for “super bronze” carved into it in several languages.
So was it that easy? No. They knew what they were looking for. They investigated any ruined building that might have at one time been a smithy. They spent about four days covering the area. But they found something that had been lost for centuries, even though others had looked there harder than they did. How do I justify that?
Divine inspiration! The alchemical spirit of super bronze was getting desperate. No one remembered how to make his aspect substance. Without it actually existing, he was starting to fade into being a legend, and he didn’t want that! So he inspired the monk who went looking (hired the party) and then led the party right to it. He needed them to find it.
My main point is this: Sometimes truly lucky things happen to adventurers. OK, really lucky things happen to adventurers all the time. Sometimes it might just be luck. Fortune favors the bold. But sometimes, it might be something else. There are a lot of gods out there in fantasy worlds, or at least angels, demons and other spirits. Does one of them benefit by the luck the adventurers received? Might they have played a hand? Maybe. Will the party ever find out? Maybe, depends on how you play the game.