Apparently psychologist Cliff Arnall came up with the name and date in 2005 based on a formula that rolled in weather, debt, time since Christmas, and something to justify it being a Monday (start of the working week) and he produced a specific day: the last Monday in January. Every year it is wheeled out again, claimed as science even though it was initiallly pushed by a travel company. All the factors Arnall identified seem to resound with many of the public so it keeps resurfacing. Of course it’s good for firms as well who want to encourage the public to cheer themselves up (by booking a holiday perhaps?) so this pseudoscientific myth continues.
But I actually like January. The nights are getting lighter and after excesses of Christmas it’s nice to have some quiet time. I don’t build up loads of debt and January days tend to be crisp and cold rather than the wet ones of December or November. So forget common senses and so-called Blue Monday. January is a great time of year.