While the first day of winter marks the beginning of the coldest season, it also marks a turning point. From this day forward, the days will slowly start getting longer again.

Historically, this was a massive psychological boost for ancient civilizations. It signified that the "death" of the year was over and the return of light and warmth had begun. This is why so many winter holidays (Christmas, Yule, Hanukkah, Kwanzaa) center around the theme of "light in the darkness."

Both are correct—they just serve different purposes.