DMs: PCs may act against the grain of what you want from your campaign.
PCs: DMs may be really twisted.
These features are part of the nature of The Game (that we just lost again).
When I DM, I like to throw in a few mundane curveballs. It’s taken me a lot of time to learn to mentally juggle the physical, emotional, energetic, PC v. DM, dynamics, and other aspects of gaming at all, but making sure to add the curveballs… that can be a doozie. What more could you do to torment your Players, really?
One time, my PCs (Human Bard, Half-Elf Ranger) picked up a young Bard who needed their help. On the way out of town, she became moody, and once on the road she had cramps… and then had her first period.
Another time, while the PCs slept, I sent a squirrel in to pick over their rations.
A seemingly “rabid” (the Players claimed) Owlbear tried to attack a PC that had gotten too close… but it turned out to be the “pet” of a local Kobold tribe.
Likewise, I have had Players mess with what I meant to accomplish. My favorite time was when my younger brother (when I placed a Scarab booby-trap in a dungeon) managed to crit twice in a row, actually catch the bug and stuck it in a wall (Elf Druid). (I was so impressed.)
So, when playing the game, be sure to include some of those “mundane” quirks in your campaign. Players enjoy them because they are so logical. Of course a squirrel would be hungry for your food, or that a hole might tear in his boot. Those things happen. Fantasy elements have their place (as a majority), but mundane effects add spice in the least obvious places.