The third Monday in January is said to be the darkest day of the year.

"Blue Monday," as this day was called by British psychologist Cliff Arnall, received this epithet primarily because of post-holiday depression.

This term was coined in 2005, as part of a marketing campaign for a travel agency, which wanted to "define" the most depressing day of the year in order to make plans for winter vacations.

She asked Arnal to define this day, and he came up with a supposed "mathematical equation" combining weather data, debt levels, time elapsed since Christmas and New Year's, and motivation levels.

The psychologist was also helped by doctor Kristin Krafod, who, among other things, said that the end of the holiday season, the expenses incurred for it, the return to work, and the cold weather negatively affect people, creating the feeling that they have nothing positive to look forward to until spring.

While reporting on this day on Monday, the BBC wrote that there is no scientific basis for considering it the gloomiest and that there are many people who question whether the third Monday of January is the most depressing day of the year.