Why is the “Law of Surprise” so important in the Witcher's world?

Question

The Law of Suprise, in the Witcher's world, is a tradition dictating that someone who saves another man's life has the right to demand, as a payment, something unknown to both persons. A typical request is "What you find at home yet don't expect", and often this would be a child born during the father's absence. This is detailed in the Witcher's Wiki and in this answer here on SF&F.

Some famous examples are those revolving about the birth and life of Ciri, or even the custom of Witchers who would use this tradition to acquire new boys to train them into new generations of mutant monster hunters.

I've read the books some time ago, so my memory is not so fresh, but in some episodes of the TV series first season, this tradition is considered something very important, almost having connotations of sacrality.

I wonder if it is ever explained (books, games or series) why such tradition is taken in such high account and how it originated, considered that often the price to pay is very high and maybe not something that the saved men would have consented to part if they could have chosen. Theoretically, this payment could even be something of low value, but we know that destiny, whatever force it could exactly be in the Witcher's world, is something very closely related to this *Law of Surprise", so this is unlikely.

Given these premises, I'm wondering why is the "Law of Surprise" regarded so high the Witcher's world? How it originated, and how it became a tradition so widespread and accepted by general consensus, when the price to pay would often be very high and demanding? Is this explained somewhere?

Answer 1

When first introduced, the "Law of Surprise" is treated as a legendary trope:

But let us not pretend we've never heard of such requests, of the Law of Surprise, as old as humanity itself. Of the price a man who saves another can demand, of the granting of a seemingly impossible wish. "You will give me the first thing that comes to greet you." It might be a dog, you'll say, a halberdier at the gate, even a mother-in-law impatient to holler at her son-in-law when he returns home. Or: "You'll give me what you find at home yet don't expect." After a long journey, honourable gentlemen, and an unexpected return, this could be a lover in the wife's bed. But sometimes it's a child. A child marked out by destiny.'

... Have you not heard of children marked out by destiny? Was not the legendary hero, Zatret Voruta, given to the dwarves as a child because he was the first person his father met on his return? And Mad Dei, who demanded a traveller give him what he left at home without knowing it? That surprise was the famous Supree, who later liberated Mad Dei from the curse which weighed him down. Remember Zivelena, who became the Queen of Metinna with the help of the gnome Rumplestelt, and in return promised him her first-born?

With dire consequences for those that violate it:

Zivelena didn't keep her promise when Rumplestelt came for his reward and, by using spells, she forced him to run away. Not long after that, both she and the child died of the plague. You do not dice with Destiny with impunity!'

But it is argued to have particular importance here not for the 'law' in and of itself, or fear of preternatural retribution, but because it was a promise made by a king:

I'd like to remind everybody of another legend. It's an old, forgotten legend — we've all probably heard it in our difficult childhoods. In this legend, the kings kept their promises. And we, poor vassals, are only bound to kings by the royal word: treaties, alliances, our privileges and fiefs all rely on it. And now? Are we to doubt all this? Doubt the inviolability of the king's word? Wait until it is worth as much as yesteryear's snow? If this is how things are to be then a difficult old age awaits us after our difficult childhoods!'

Note that there is a further twist as detailed by Geralt (it is left ambiguous whether or not this is a historical rule, or a bit of creative licence by Geralt):

Roegner knew the power of the Law of Surprise and the gravity of the oath he took. And he took it because he knew law and custom have a power which protects such oaths, ensuring they are only fulfilled when the force of destiny confirms them. I declare, Urcheon, that you have no right to the princess as yet. You will win her only when—'

'When what?'

'When the princess herself agrees to leave with you. This is what the Law of Surprise states. It is the child's, not the parent's, consent which confirms the oath, which proves that the child was born under the shadow of destiny.

Answer 2

This is not that different from the model that was shown in The Godfather.

Vito Corleone: Good. Someday—and that day may never come—I'll call upon you to do a service for me. But until that day, accept this justice as a gift on my daughter's wedding day.

Bonasera: Grazie, Godfather.

Same principle: in return for Corleone's assistance in avenging his daughter's beating, Bonasera owes Corleone an unspecified future thing. Neither Vito nor Bonasera knows what it might be, or if it will ever even occur. As it happens when that chip is called in it isn't something illegal or even questionable. It's simply making sure Sonny's body is presentable for his funeral.

The world of The Godfather is one where such a situation is respected by all involved because of the power Don Corleone wields that would make breaching that agreement a Very Bad Thing. The Witcher simply uses the same model where instead of the local crime lord, it's Destiny that has an actual presence that will screw you over if you try to renege. Under such circumstances, of course trying to evade the results would likewise be a Very Bad Thing and such a promise would be respected.