A typical story finds the MC in a certain status quo (both for the character themself and for the world around them) and ends with the MC having overcome a series of events. At the end, there is a new status quo for the MC and, maybe, for the world around them.
What is the objective of this typical structure? To tell a satisfying story of growth and, possibily, self-discovery.
Why would one want to break away from the rule? Well, it'll depend.
"Eveline", in James Joyce's Dubliners, presents the story of a young woman stuck in a despairing life. She has one chance to break away from it all but, at the very end, she ends up not taking the step forward. She went through the events that would allow the character to grow and attain a new status quo and, instead, shrank from the change and remained as she was.
What effect did the 'break from the mold' create? The image of a person who, given the means to save themself and start a new life, is unable to do so. Perhaps the author wants to point out some people are impossible to save, or perhaps the fault was the world around which effectively twisted the MC into a helpless being, stripping them of the imagiantion and will to swap despair for hope.
So, if the objective of the author is to focus on the reasons why a person/character would refuse to improve themself or their situation, this is a good option.
Although I can't think of an example, another situation would be the MC who strives to change the status quo of the world around them. A rebel freedom fighter, for example. The tale would start off with a tyranical world and a group of fighters trying to change the social status quo. But perhaps, through all the events, all the fights, the rebels end up exactly where they were and the dictatorship remains as unshakable as at the beginning.
There may have been growth for the main characters. Personal goals may have been attained. But the fact remains: both the rebels and the dictatorship are still in the same spot. Perhaps the moral is that a group of freedom fighters cannot succeed because it takes an entire people to raise their collective head and fight.
Or perhaps it's a serial story and the only growth is within the characters, with a token victory - or defeat - thrown in occasionally. Of course one would expect the status quo to change eventually. Slowly. Perhaps suddenly at the end of the series. Nevertheless, there would be a lot of episodes where the characters would go through the motions without any change to the status quo.
One could play with partial status quo changes. I think the first film of the Matrix (have never seen it but have heard a lot about it over the years) may fit the bill. The status quo of the MC (Neo) changes as he stops being a normal person and becomes a warrior, but the world around him is still the same. This particular example works because the goal of the characters is to radically change the status quo of their world.
Another example would be the opposite: the efforts to change the status quo of the world around are successfully but the MC remains essentially the same. So you'd start with a warrior fit to live in a warring world but, as the world shifts from war to peace, the warrior stops belonging in it because they didn't shift their ways. This makes me think of countries ravaged by war for so many generations, that people may have difficulty re-imagining themselves -and re-making themselves - as anything other than soldiers, killing, pillaging and destroying. Literally, because that is all they have known.
For one to break away from the rules, one must understand why those rules exist, what they create. Once one understands them, then one can twist them in order to create something different but very specific.
Above all, know why you want to break away from the mold. Then you'll know when and how to twist the rules.