In the winter especially, you go to work in the dark. Spend all day indoors with no windows while the sun is out. And then drive home in the dark to a dark house.
You get so depressed and lose motivation. And what did you gain? Less money than last year.
Whether this fixes the OPs issue or not, this is a valuable post and my future self thanks you for making it as I'm sure I'll hit similar problems eventually. And I thank you now!