1. December is winter in the northern hemisphere. In fact, the winter solstice—the longest night of the year—is usually the day after my birthday. It’s dark. It’s cold. And people are starting to wind down into hibernation mode to finish out the calendar year and ride out the season. It makes it difficult to want to do anything, and it also limits what you can do (definitely no pool parties or ice cream cakes growing up—I was always jealous of the summer birthday kids!).