The shadow is the psychological idea that every human has a part of themselves that is wholly based on the idea that it is the half of your personality that is based solely on desire. The shadow isn't bad, hiding the shadow entirely isn't healthy as is completely bowing to the shadow isn't good either.
And I am firmly convenced into the idea of all manner of stories are usually made better with the implimentation of a shadow. Like for examples anti-heroes.
Alright, so there is a few different descriptors of how Anti-heroes are used to describe. You have the earler meaning of a hero who is not really good at being a hero. Than you get the silver age ideas of heroes who do morally bad things but for good reasons.
But regardless, all of these archtypes require a shadow of some kind. It is vitial to good character design, as well, it is how real people work and how to make it realistic to fleshed out characters.
Not every anti-hero has been written in a manner that includes a shadow. I mean this as nicely as I can, if your anti-hero does not have an aspect of darkness to it, you're just writting an edgy hero at that point and no even a good hero at that.
Being an anti-hero is a fasinating idea over all. The idea of doing what is overarchingly right but morally wrong is interesting. Most people can't always make the perfect correct choices, and most people have the urge to carry out justice in any manner ignoring morality. Anti-heroes mostly fall into those sections.
But, there is a moral issue still. Doing what is morally seen as right, what feels right and what is the best over-arching idea is not always the same actions. As a result, that is a fasinating moral issue. Is doing what feels right more important, or is doing what is morally right more important or is doing what in the long run would be morally right more important.
And realistically, all of the options can be understandable outcomes. Humans aren't perfectly moral entities, and as a result how we react to things can vary. Hence, anti-heroes being fasinating.
Take John Wick for example. He is not a morally upstanding person, but his behaviour is sometimes seen as understandable. He is also an anti-hero. He's behaviour is interesting because he has a shadow. Killing people is usually seen as bad, killing people for revenge is still seen as bad, and that's where all the fun of an anti-hero is.
Characters like Superman is fun because they have strict moral bounderies, but they can't play on the sliding morality scale while anti-heroes can. When you have characters like The Punisher or Dexter, they are more interesting because they flirt with being way more morally messed up.
Take Shadow from Sonic. While he isn't as brutal as the other examples, he is still an example of a character who is deeply based around his shadow. He has understanable hatred against Robonic and a desire to prove he is the Ultimate Lifeform, but the interesting part is seeing where he draws the line. How far is he willing to go before he counts that as too far.
Morally grey characters have to consistantly balence their behaviour. A character fine with torture and murder might not be fine with harming woman or children. Or a character might only be fine with hurting guilty parites and would never hurt and innocents.
Dear reader, you know who you're dealing with. I don't like how some anti-heroes are written. If your anti-hero isn't partically wrong it feels hollow. My first thought as an example is IronHeart. Note, I did not watch the full series, I only watched until about halfway. But so far, she has had no signs of the plot showing the ramifications of her actions.
She steals stuff and no one really cares? Oh, what's that? The person she stole from was actually evil? Really? What a cop out. Theft, even if it is targeting a rich person, effects so many people. Employees loosing jobs for one. And our hero has no consideration for that? She just... Doesn't care? Hell, even my darling genre of heist movies make it somewhat clear that the theives are out-of-line. Perhaps sympathetic but still out-of-line.
Or maybe another example. Riri more or less blackmails a black-arms-dealer into giving her free tech, but like... That's cool, he was a black-arms-dealer who is just some nerdy bloak. No moral conudrums there, huh? I mean, come on. That can't be seen as just, fine, right? Blackmail is blackmail regardless of context. Yes, you can argue that it's a taste of his own medicine and what not, but two wrongs rarely make a right.
And I really don't get it. I think they were worried about making Riri come across as a bad person but like... We liked Tony Stark and he wasn't a boy scout. At the start he is a womanising rich guy who profits off of war. Very little Riri would do would make her close to Ironman 1 levels of bad. Tony was never a good person, he was eventually a better person, so why is Riri not given the same chance?
I think there it might be a case of people wanting to write non-perfect heroes but still want them to be proper anti-heroes. Ironically enough, the end result is someone who is harder to like than a regular anti-hero or a normal hero.
So, word of advice, just write a character as best as you can and don't worry about making them likeable over letting them be people. People are messy, the characters people tend to like are also messy. So, just write.