While the spring, summer and even fall are enjoyable in Brussels, the winters are rough here. Similar to places like England, it's almost always rainy and overcast, which makes for a gloomy winter and means you can go days without really seeing the sun all day. It gets darker even faster in the Scandinavian countries where it's pitch black outside by 4:00 PM or 5:00 PM.
Given the capricious nature of Brussels' environment, I've been told to always carry two things with me - sunglasses and an umbrella. You never know which one you'll need on any given day! As for the long winter days, people know what to expect. It's nice that it's also around the holidays, so there are other ways to cheer up by spending time with family or looking forward to the Christmas Markets, which will open very soon here!