I think every character, no matter how insignificant, has an arc (or at least deserves one). A common trope among writers is to use pain to make their protagonists suffer, and while this isn't necessarily a bad way of showing struggle, pain by itself doesn't mean development. In fact, too much pain can break a character beyond repair, and they might never be the same again after the events of the story. I've always been interested in psychology, and while I'm no expert in it, I enjoy reading the material psychologists publish. The human condition is interesting, which is why we write about it! Anyway, realistically speaking, different personalities handle trauma and their past differently, and how they move beyond their harsh times. All in all, it depends on the person: Do they sulk and go to others when they struggle, or do they go on stoically and keep their emotions bottled up until one moment shatters it? No matter the answer, there are pros and cons to each.
It's easy to focus on a character's failures, but our minds are better at figuring out what's wrong over what's correct, so we can use that to our advantage. From our failures, we can figure out what we want our characters to succeed at. Are they someone who's attempting to run the family business and hewn their charisma? Maybe they're a brilliant scientist who's trying to ignite telomere production within the human body so that people no longer age, or maybe they're an adventurer who turns into a competent warrior. Each archetype and personality you can think of has its benefits and its drawbacks. Personalities often gravitate toward certain jobs as well, so consider what your characters might be good at, experienced with, and what they might know. You can argue anything else is fair game.
I often have to write characters that are smarter than I am, but it's not as hard as it sounds. People will have a list of what they think a "genius character" might be, but you are the writer. You get to decide how the problem they're facing is solved and how quickly, as well as what the character is knowledgeable in. If you don't know much about chemistry and yet your character is a fantastic chemist, research more about chemistry! Whatever the topic they're proficient in, it helps to learn as well, and that's where the scientific/mathematical part comes in. Not only does that help your writing, but it helps to know certain information for your own purpose as well. Intelligence is only one piece of the pie, of course, and we have to consider that good characters are complex, three-dimensional beings that are not only flawed but that they contradict themselves in their personality. A common theme with this in intelligence is having someone who's "book smart" (good with academics, hard facts, etc.) versus someone who's "charismatic" (good at understanding people, social cues, emotions, etc.). But these two are not mutually exclusive in the slightest: there's a reason why the scariest villains are brilliant and well-rounded in their intelligence.
Furthermore, let's consider that some characters might be good fighters. I'm not saying you should go out and fight someone to get that experience as a writer, but I was in that position where I was writing action scenes and had to learn my formula to make it interesting. Of course, it depends on your story, but if you have an action scene in first person, this is the most limiting factor, but it also lets you experiment with interesting ideas. I often rectify these ideas by having duels in first person. I listen to heavy music and know a lot of history about the samurai, and so it helps to understand how those types of "Last Stand" or "Legendary Duel" battles go, especially with swords. We love swords!
Anyway, based on what your character is good at, bad at, you have to consider beyond simple backstory "what's at stake". Let the reader see what's at stake, whether that be from your godly point of view, or from the eyes of the protagonist. Perhaps your character isn't necessarily proficient in the right skills to deal with what's at stake, and your book's journey is that of a learning experience. Maybe your character is already experienced, and as a result the threat is far more pressing, and that's why it requires them. Why do they always hire the retired detective in movies? Because he has to close out his last case using his mind: he's the one with the most experience and can bring them to victory. I'm not saying you should follow Hollywood's formula, but to write, it's not a bad idea to have something of the sort. Or for a grand epic, maybe you have to mix both elements: your character starts out inexperienced, becomes experienced, and then the second act of the story requires them destroying the evil. There's a reason this is popular!
Growing up, I always loved playing the protagonist in a videogame that could always do cool combat moves, the one that embarked on a journey to stop evil from enveloping the world. When you're a kid (and I still enjoy these to this day), you can play plenty of Super Mario games and see why Mario has to defeat Bowser. It's because Bowser wants to control the Mushroom Kingdom and marry Princess Peach, and it's up to Mario and Luigi to traverse eight biomes to get to his castle, with each biome getting more and more difficult. In Super Mario Wii, for example (which is probably the first game I ever played), they call the biomes Worlds (not unique to this Mario game). When you get to the final battle after going through the eight worlds, Bowser makes himself nigh-undefeatable, and it's up to Mario to find that one thing that stops him after defeating all of his lieutenants before. There you go, Mario saves the day, gets Princess Peach, and the Koopas are defeated.
Everyone knows of Super Mario, of course, and there's a reason he's so ingrained in our culture. Everyone wants to be a good guy like Mario and save their home. It sounds extremely basic, but there's a reason they've been releasing these games since 1985 and have no intention of stopping. It's because the platforming games are a classic, they took inspiration from different parts of existing media and created something completely unique that has both characters (in this case, players) that get stronger and mend their weaknesses, all while the stakes are to defend the world from Bowser. Rarely you'll ask for Bowser's motivation outside of stock evil, but in any case, it's one of the most basic examples I have of victories, failures, and stakes.
I hope this helps no matter where you are in your writing. If not, enjoy my Mario tangent!
Until we meet again, stay cool,
Dustin