If you live in the Northern Hemisphere, December 21st is the shortest day of the year. It has to do with the tilt of the Earth, and its motion in orbit around the sun. Astronomy 101. But ask any demigod if the Winter Solstice is a short day and they’ll scoff, and then start to panic-sweat a little. Here’s why:

It’s when Hades comes to visit.

Hades was allowed entry into Olympus on only one day: you guessed it, the Winter Solstice. On all other days he was running the Underworld — by himself — while his brothers Poseidon and Zeus enjoyed lives of luxury! Safe to say that the Hades who shows up every year at Olympus is not a gift-bearing, high-fiving, Hades.

It’s when the Master Bolt was stolen.

Percy’s entire first quest was set off on the Winter Solstice, thanks to Luke stealing the Master Bolt. Maybe it was fun to read about, but think of the multiple near-death experiences Percy, Annabeth, and Grover had to endure while trying to retrieve that thing and bring it back to Zeus.

It’s when Percy and Thalia almost got destroyed.

Thanks to the prophecy that a child of the Big Three (Zeus, Poseidon, Hades) would be responsible for the fate of Olympus, the Winter Solstice became the occasion when the gods convened to determine the fates of those pesky demigods. The scales of justice tipped in favor of Percy Jackson, son of Poseidon, and Thalia Grace, daughter of Zeus, when Hades decided to skip his annual visit to Olympus that year. Close one.

It was a deadline for the Heroes of Olympus.

Roman demigod heroes Jason, Piper, and Leo had until the Winter Solstice to save the world from an array of angry gods. Imagine the stress! On their first mission, the team had to travel to Wolf House and free Hera from captivity. This brave act thwarted the earth mother Gaea’s villainous plot and brought order back to the Olympians, who were acting like impetuous brats without the goddess of motherhood around.

So, happy #WinterSolstice demigods. If you make it through the day then the odds are you’ll make it all the way to the next year.