Let's delve into the story of Blue Monday – through literature, marketing and a little common sense, there's a lot to be learned, even from the lowest moment of the year.
It all started with songs that called blue the colour of sadness, then came an association with Monday moods, and eventually a marketing team invented Blue Monday as a fixed annual event. But Blue Monday is a good opportunity to dedicate some space to the feeling of sadness and then use it as a reason to do something good for ourselves, those around us and also for the place we live.
Why the blues?
"Wyth teres blewe and with a wounded herte" are the words that the English writer Geoffrey Chaucer (1343-1400) - most famous for The Canterbury Tales - uses in his short poem The Complaint of Mars. That 'blewe' stands for blue and refers to 'teres', the archaic spelling of 'tears'; so 'blue tears', which means tears of sadness.
That's considered the first time that blue was associated with this particular mood. But English literature soon records other episodes in which the colour blue is associated with illness, perhaps because of its association with the colour of the cyanotic faces of sick people and corpses , but also with demonic possessions and alcohol abuse . There are many examples, but to make a long story short, blue became - in time - the colour most closely associated with sadness, while a new style of music, born in the United States took the name 'blues'.
Anyone familiar with the typical working week doesn't need too much explanation here, but it's worth taking a quick look at how Monday is associated with the difficulties of getting back to work after the weekend break.
In Turkey, there is the 'pazartesi sendromu', or 'Monday syndrome', the same that affects French workers who are used to answering 'Comme un lundi' when asked how they feel when they return from the weekend. Similarly, in Anglo-Saxon countries, to describe the bad mood of those who show up at the office in a bad mood, they say 'have a case of the Mondays'. [...] A very popular saying in German car manufacturers, on the other hand, goes 'montags-auto', or 'Monday cars', thus indicating those defective products whose imperfections are attributed to the lack of sleep experienced on Monday mornings. Finally, in Spain the beginning of the week is the 'día de bajón', i.e. the 'day of collapse', while in Portugal it is 'el dia cinzento', the 'grey day'. 
Blue Monday in music
The history of contemporary music tells us of two famous Blue Mondays, one of which inspired the other.
The first Blue Monday is a song originally written by Dave Bartholomew, first recorded in 1953 by Smiley Lewis. However, what made it famous was Fats Domino who re-recorded it in 1956. The song was a huge hit at the time and became one of the first rhythm and blues songs to enter the Billboard charts.
The other famous Blue Monday is by New Order (1995). Peter Hook, one of the songwriters, said: I was reading about Fats Domino. He had a song called Blue Monday and it was a Monday and we were all unhappy so I thought, 'Oh, that's quite apt'.
Marketing invents Blue Monday
The English term Blue Monday ('sad Monday') refers to a particular day of the year, usually the third Monday in January, believed to be the saddest day of the year for people in the northern hemisphere. The concept was originally made public in 2005 in a press release by the British TV channel Sky Travel, which claimed to have calculated the date using an equation. The whole idea falls into the realm of pseudoscience, and the underlying equation is considered to be without any foundation .
Despite the attempt to attribute a scientific value to this statement, the truth is that no equation has ever established the amount of sadness of one day compared to another. This is, of course, common sense, the same common sense that we can use to take a step beyond marketing and use this specially created occasion to do something good with it.
Making sense of Blue Monday
A day like Blue Monday, even if it is a marketing invention, can offer an opportunity to reflect on a condition that so many of us have in common these days: a sense of discouragement about what we are experiencing (we only have to open a newspaper and read the news about climate change, wars, global economic difficulties, to understand how easy it is to give in to sadness).
But if it's good to reflect on the current state of the world, we believe it is even better not to deny sadness, a feeling that is part of us and can help us to see where we often don't want to look. What we believe is important is to let ourselves be guided by the desire to react, and turn despondency into positive action. How? There are many ways: from dedicating time to ourselves and the people we love, to doing something to improve life around us. Even planting a tree can be a great way to turn Blue Monday into Green Monday. Not to fight sadness, but to turn it into positive action.
That is why we say: let's green the planet... and this Blue Monday too!
 John Dryden (1631-1700) wrote the following lines in the play All for Love (London, 1678):
Now, my best lord, in honour's name, I ask you,
For manhood's sake, and for your own dear safety,
Touch not these poisoned gifts,
Infected by the sender; touch them not;
Myriads of bluest plagues lie underneath them
 In Letters on Demonology and Witchcraft (London, 1830), the famous Scottish poet and novelist Walter Scott (1771-1832) wrote of: "...the dissipated and intemperate habits of those who, owing to a continual series of intoxications, become subject to what is popularly called the Blue Devil, cases of this mental disorder may be known to most of those who have lived for any period of their lives in societies where heavy drinking was a common vice."