I think there's always a logical explanation to all human behaviors and feelings. For example, have you ever experienced a kind of morbid depression during Christmas holidays? In persons affected by a mood disorder this is generally due to the season's transition occurring during December, when the overall amount of daylight is dramatically reduced to its minimum, at least until the end of December. In persons without this kind of problems, social and environmental factors may actually affect their way of living. Generally, the truism about the fact that during Christmas holidays you must be happy because everybody's happy is rooted in the view of life that today most media use as their own Gospel. This view desperately tries to hide the simple and obvious truth about consumerism that so clearly has been expressed by Irvine Welsh in Trainspotting: live, consume, die.
But there are people who think differently: why should I follow this line? why should I be happy only because the media's Gospel tells me that it's Christmas? Why should I buy something new? Why should I consume? And what is at the end of the line? Christmas holidays force this kind of people to face the fact that they're a minority. And they actually feel lonely. And when you feel so, the shadow of sadness silently slips under your door. The solution is to turn this sadness into energy, trying to find if there's actually an end to this line. Finally, these people conclude that there's no line at all. And if you want to, Christmas is every day.