Sometimes it's funny when tabletop RPG players expect the game to behave like a video game.
GM: "The nearby town sent a message that a swarm of zombies is coming down the haunted mountain for them! They need help!"
PCs: "Cool. But let's finish that mushroom side quest first, and then we gotta help our wizard buddy get his new broom tuned up."
GM: "...okay."
PCs: "Ok, what do we see when we get to that town?"
GM: "Seems like everyone's dead. Looks a swarm of zombies or something came down from the mountain and ate everyone alive or something, maybe a day or two ago."
PCs: <confused, shocked>