Humiliation is an interesting emotion. Assuming we’re not discussing about the fetish of humiliation but ACTUAL humiliation — it is an incredibly valuable emotion. especially for character development. Consider, why do you feel humiliated? Mostly it is because you have just LEARNED something, or more likely been FORCED to learn something, that you really wish wasn’t true. It is also highly correlated with naivety which is a character trait that is very common in the first few arcs of web novels and contemporary literature.
Let us examine your example, or a generic one like it. A MC saying, “I will protect XXXX!” followed by someone beating the crap out of him, and thus humiliating the MC. The MC had a false sense of reality — that he was powerful enough to protect someone or perhaps that the world had a thing like justice, whatever. Then he had his perception of reality shattered and was forced to realize a truth that he wishes he never had to learn — that he is WEAK, that there is no justice in the world, etc. Where a novel will succeed or fail is not so much this setup of being “humiliated”, which is a normal emotion that EVERYONE WILL EXPERIENCE IN LIFE, but in how the MC deals with it.
There are tons of avenues for the MC to follow that are all equally as valid from a story telling perspective, too. Perhaps he realizes the inherent unfairness of the world and starts to travel the path of a misanthrope — in this way he is seeking to gain power not so much to fulfill his original goal but so that he will never have to be confronted with the harshness of having his perception of reality shattered. This is a “bad” path for the MC but perhaps a great one for the story. Why? Because there are an endless number of ways for the MC to have a fundamental misapprehension about reality but he is acting as though if he is “strong” enough he will not ever be forced to realize he is wrong because there will be nobody that can effectively actualize any force on him. This is the general path of most antagonists in stories, Darth Vader for example.
The “good” way which is not surprisingly much rarer (again, for the MC) is for the MC to integrate the experience and internalize it. From a psychological point of view you have to let that part of you that was wrong, tricked or mistaken DIE, and is it ever easy to let part of yourself die? To face the facts that you were naive, lied to, or just stupid? Many people desperately hang onto delusions just to avoid admitting any of these things to themselves. Consider, you have probably read stories or even had experiences in your own life where something traumatic happened, the MC or you overcame it and then later someone mentions to you that you seem like a totally different person. That is because YOU ARE! Part of you died, you fell into the abyss of your persona and ego and then rose from the depths a new and changed person!
The only incorrect way of handling humiliation for a character is if nothing changes with regards to their character at all. In that case there really was no point at all, except if you’re using humiliation without any change to demonstrate that the character is really beaten down almost past the point of redemption, i.e. a character that has given up all hope, for example. And even that is only useful/good if it is used for some later payoff, in my opinion.
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Lastly, I just want to say that a lot of people confuse humiliation with degradation. The nuance is totally different!
Humiliation should be an inflection point, a chance for change be it positive or negative for a character but definitive change.
If you’re writing a scene featuring a character being humiliated always ask yourself, is this humiliating or just degrading them? The latter is mostly pointless unless you’re writing trauma porn.