Joyce Byers is the protective mother of Jonathan and Will. As a single mom, she has a lot on her plate and does the best she can with what she's got. She's hardworking, pragmatic, loving, and fiercely protective. In fact, she takes on a maternal role for many of the young characters in Stranger Things, not just her sons.
Joyce is someone others can trust. She's always willing to listen - when she's not wrapped up in her own problems, that is. Especially when Will is in trouble, Joyce is frazzled and all over the place. She's not always the most reliable of people and can get lost in her thoughts and head. Luckily, she never gives up and is almost always correct in her theories.
BEST: Tenacity
The trait Joyce is best known for has to be her tenacity. She never, ever, ever gives up or lets go of matters until she proves the disbelievers wrong. No matter how far-fetched her theories are, she usually ends up being right.
Joyce will go to the ends of the Earth to get what she wants, which in most cases, means saving Will or figuring out the mystery of the Upside Down.
WORST: Stubbornness
Joyce's tenacity isn't always a good thing. Sometimes she is so set on completing a task that she forgets everything else, including her basic responsibilities as a human being. She seems to get tunnel vision, blocking out the rest of the world and becoming utterly fixated on her investigations.
As a result, she sometimes forgets to take care of herself and her family. She brushes other people away, like Hopper, and almost loses her job. Her stubbornness also causes many arguments between Joyce and her loved ones, but she alone can't be blamed for that.
BEST: Trusting
One of the reasons Joyce gets as far as she does in her investigations is that she is open-minded and willing to trust other people. For instance, she trusts Alexei when nobody else will, and has no second thoughts about Eleven when they first meet.
Of course, sometimes this proves to be a weakness, too. She trusts Jonathan to be home and look after Will the night he goes missing, and she trusts Hopper to look for him, but he doesn't take her seriously at first.
WORST: Self-Absorbed
Though this weakness is something Joyce is aware of and even admits to, it can hurt other people. She is often so deep inside her own mind that she has no idea what's going on around her.
In season 1, she almost neglects Jonathan because she's so fixated on finding Will. She doesn't realize that other people are going through things, too, even her own son. Of course, this fault is understandable, but it's still one of her worst traits.
BEST: Caring
No matter how closed off Joyce can become, she's always driven by her deep care for other people, particularly her family. Everything she does, she does with her children in mind. She goes so far as to destroy her house in season 1 to find clues about Will's location.
Even when she isn't in the middle of a life-or-death quest, Joyce takes the time to show people she cares. Eleven is someone she tries her best to accommodate, knowing the harsh background she's come from. Joyce comforts her, listens to her, and tries to help her feel safe.
WORST: Disorganized
Joyce becomes so fixated on single tasks that every other aspect of her life is thrown out the window. In season 1, her entire household becomes a wasteland, Jonathan is left completely to his own devices, and she forgets she's an employee at a store.
Apart from her disorganized physical surroundings, Joyce's thoughts and priorities are also out of balance. She worries so much that she forgets to live in the present. She doesn't take care of herself at all and falls back on commitments involving other people. Hopper is one of these, and he fails to realize that she didn't just stand him up, but she also fails to explain herself.
BEST: Determined
Once Joyce forms an opinion, she will stop at nothing to prove that she's correct. In season 1, she strings Christmas lights up around the house and convinces herself that she's speaking to her son through the lights.
In season 2, she plasters Will's drawings around the entire house, convincing everyone that she's gone off the rails. But Joyce doesn't care what others think of her, because she has set her mind to completing a certain task.
WORST: Overly Conservative
Joyce hates change - not just negative change, but any change. She would rather feel safe and secure than take a risk that could lead to happiness. The perfect example of this is her choice to date Bob.
No matter how kind he is, he doesn't exactly offer any excitement. Jonathan and Will don't have any strong feelings about him, and it seems that what Joyce loves most about him is how safe he is. Part of the reason she is afraid to be romantically involved with Hopper because it's a risk and a change.
BEST: Compassionate
Joyce has a unique ability to understand other people, even if she doesn't always use this ability. She is very compassionate and, when she's in the right headspace, will give her undivided attention to people.
She tries to be there for Jonathan, Will, Eleven, and Hopper. Especially in season 3, when she is much more emotionally available to help others, she gives her time to listen to Hopper and advise him on what to do regarding Eleven and Mike.
WORST: Overprotectiveness
One of Joyce's biggest flaws is her overprotectiveness. Will is treated like a child much younger than he is, which is why he still wants to play D&D in season 3 when all of the other boys have moved onto other things.
Perhaps a large reason for this is his disappearance, but Will even lashes out a few times, wishing people would stop treating him like something is wrong with him. Joyce is one of these people, though he still loves her very much.