Seeing the new fear system and knowing that fears come to the base game and some from High School Years...
Knowing the sentiments, it seems like older packs won't get their own fears, even though they are full of possible fears.
And what a surprise! This fear turned out to be true!
So, I'll suggest some fears that could come from other packs. Feel free to suggest yours!
-Fear of Bears - After losing a fight to a sim in the bear costume, these sims will run away from sims in the bear costume and will stop their adventure in the bramble path when encountering a bear.
-Fear of Camping - Going rough has left the sim scared of what might happen. With just a tent covering them, who knows what creatures may come and attack them. They will be hesitant to sleep in tents and will wake up easily when sleeping in one. When going to Granite Falls with them, it's best to rent a cabin instead.
Get to Work:
-Fear of Aliens - After being abducted by aliens, these sims will feel uneasy around aliens, will always react negatively to discovering an alien, and will avoid contacting aliens.
-Fear of Doctors - After being a victim of malpractice (due to being falsely diagnosed), these sims have a hard time getting along with doctors.
-Fear of Detectives - After being falsely accused, these sims have a hard time getting along with detectives.
-Fear of Scientists - After "participating in cruel experiments", these sims have a hard time getting along with scientists. They will also always refuse to try out scientist potions and will always refuse to have their DNA taken.
-Fear of Being Unprofessional - After malpractice (doctor), false arrest (detective), failing often (scientist), or earning no medal at work, these sims will be more hesitant on making professional decisions and will often need a second opinion. After all, mistakes in this field of work can be really bad...
-Fear of Saunas - After almost dying in a sauna, these sims will avoid them.
-Fear of Mazes - After encountering a ghost while navigating the maze at night, these sims will avoid the maze at all costs.
-Fear of Being Outcasted - That was close! Breaking the rules can lead to be kicked out of the club, and why lose all that awesome time and sims by a stupid reason? These sims will never break the rules and will feel extra bad should they find themselves breaking one.
-Fear of Being Overthrown - Things aren't going well with the members, and as a leader of the club, it could as well mean being overthrown and losing the leadership. They dread the day when that comes, being constantly tense or scared while gathering. There are two ways to overcome this: by raising relationships or by losing leadership.
-Fear of Dining Out - After getting food poisoning from dining at a restaurant, these sims won't feel comfortable the next time.
-Fear of Candy Bowls - Any candy bowl seem scary after being jumpscared by one. Suspect anything!
-Fear of Singing Karaoke - After an embarrassing performance, these sims won't be likely to sing karaoke in public again...
-Fear of Fireworks - After a firework mishap, these sims avoid fireworks at all cost. Even sparklers.
-Fear of Talking Toilets - That's it! After being splashed by a rude talking toilet, these sims swear that they'd rather have a bladder failure than use a talking toilet ever again!
-Fear of Earthquakes - After an earthquake that happened while the sim was scared, these sims will pass out when an earthquake happens. (Pass out part comes from the fact sims already get scared from being on a lot with the earthquake trait)
-Fear of Vampires - After being drunk from a vampires, these sims take extra measures to avoid them and keep them at bay.
-Fear of Being Cured - This comes when another sim tries to slay (cure) the vampire but fails. This could give the fear of being cured which makes vampires avoid sims that have the cure in their inventory or know how to make the cure.
Movie Hangout Stuff:
-Fear of Horror Movies - After watching a horror movie while being scared, these sims don't want to see another horror movie. That won't happen to sims who have declared horror movies as their favorite.
Romantic Garden Stuff:
-Fear of Wishing Wells - After getting a deadly outcome, these sims will never throw a coin in any well or water fountain.
-Fear of Punishment - Being disciplined a lot in one day has taken a toll on the child. They'll either be on their best behavior or go wild with no parents around.
-Fear of Parenting Judgments - This sim got bad looks when their child misbehaved in the public. These sims will feel nervous when out in the public with their child and will automatically discipline them when they misbehave.
-Fear of Raising a Failure - Seeing how bad is their child performing in the school or overall doing in their life, these parents have to take stricter measures in order to ensure that their child will at least have some chance in life. Expect automatic punishments and constant worrying.
-Fear of Diary Peekers - Yikes! This sim caught another sim reading their diary. That is bad... From now on, these sims try to hide their diaries in the most obscure places (which can be found with self-interaction) and will not feel great writing near other sims. Thanks to this, these sims will also struggle to write novels near other sims.
-Fear of Growing Up - The adult life seems so intimidating to the sim. It would be great if they could never become an adult. With this fear, children and teens gain responsibility slower and lose it faster. Once an adult, these sims will act like they have Irresponsible trait even when they don't have it as long as they have this fear.
-Fear of Seeming Uncool - Having good manners got the sim mocked for it. This has taken a toll on them, so children and teens gain manners slower and lose it faster. Once an adult, these sims will act like they have Bad Manners trait even when they don't have it as long as they have this fear.
-Fear of Being Weak - After other sims were rude to them, these sims want to stand up for themselves. With this fear, children and teens gain conflict resolution slower and lose it faster. Once an adult, these sims will act like they have Argumentative trait even when they don't have it as long as they have this fear.
-Fear of Being Taken Advantage Of - This sim helped another sim, but all they got in return was hurt. Due to this terrible thing, these children and teens gain empathy slower and lose it faster. Once an adult, these sims will act like they have Insensitive trait even when they don't have it as long as they have it.
-Fear of Being Unheard - Being calm has left the sim feeling that staying that way will have them be unheard. In an attempt to be more heard, children and teens gain emotional control slower and lose it faster. Once an adult, these sims will act like they have Uncontrolled Emotions trait even when they don't have it as long as they have this fear.
Cats & Dogs:
-Fear of Cats - After being attacked by cats, these sims avoid cats. Won't come to cat lovers.
-Fear of Dogs - After being attacked by dogs, these sims avoid dogs. Won't come to dog lovers.
My First Pet Stuff:
-Fear of Rodents - After having Rabid Rodent Disease, these sims will stay far away from any rodents. Even mice from mouse holes make them run away!
-Fear of Water Slides - After failing horribly on a water slides, these sims prefer to not even look at one.
-Fear of Birds - Feeding birds is no longer doable after being attacked by birds.
-Fear of the Jungle - After being a victim to jungle dangers, these sims constantly feel scared in the jungle.
-Fear of the Temple - After falling into temple traps, these sims feel constantly scared in the temple.
-Fear of Bees - Bees just keep attacking sims. It is better to avoid these vengeful insects!
-Fear of Skating - Falling a lot during skating has sims avoid it at all cost. They will also get injured more often in Mt. Komorebi during icy conditions.
-Fear of Snow - After being in an awful blizzard, these sims dread stepping outdoors during snowy weather. Won't come to sims who have declared love to snow, but will more likely happen to sims who have declared hate to snow.
-Fear of Water Gardens - After falling into a water garden filled with sharks or piranhas, these sims stay as far as possible from water gardens.
-Fear of Fame - This sim has seen the bad side of the fame. Perhaps it is best to step out of the spotlight...
-Fear of Sleeping Pods - After being pranked in a sleeping pod (either they were locked in or their dreams were hacked), these sims would rather sleep on the ground than in a sleeping pod.
-Fear of Money Vaults - After being trapped in a money vault, these sims won't step into one ever again. All the money there is lost anyway!
-Fear of Creepy Fans - After receiving a creepy message (Public Number quirk) or encountering a stan (Stan quirk), these sims will always be tense near fans. The creepy one could be there among them...
-Fear of Losing Relevancy - These sims enjoy their spotlight, so when their fame begins to fade, they'll panic. These sims become really tense when their fame begins to go down and can do an emergency social media update to stay relevant, which could lead to embarrassing moments. And should they step out of the spotlight, the sadness that comes from that never goes away.
-Fear of StrangerVille - Something is definitely not right with StrangerVille. After a scared visit, this sim feels unsafe is StrangerVille. The further the story has progressed, the more unsafe will the sim feels. They can overcome this fear once the story is completed.
-Fear of Oceans - After being pulled underwater by the ocean threat, these sims won't step into another non-pool body of water ever again.
-Fear of Mermaids - After barely escaping a mermaid attack, these sims won't feel safe around fishy sims... As soon as they spot one in the ocean (even when not in mermaid form), they'll get out immediately.
-Fear of Volcanoes - After touching a volcanic bomb, these sims will stay far away from any volcanic activity.
-Fear of Island Spirits - After being cursed by island spirits, it is a great idea to stay away from lots that are known to have those spirits.
Realm of Magic:
-Fear of Spellcasters - After getting a part of nasty magic, these sims avoid spellcasters at all cost. When they happen to be in the Realm of Magic, they will be extra scared.
-Fear of Overcharging - After surviving an overcharge. this sim will avoid casting magic when their charge is high up.
-Fear of Roommates - After a nasty roommate, these sims will never get another roommate again.
-Fear of Plagiarism - After getting caught with plagiarism, these sims think twice about doing that again. It could end up terribly...
-Fear of University Rivalry - This sim just wants to study and they get slack by other school's students. Due to this, they're having a hard time building relationships with students and alumni of the rival university.
-Fear of Britechester rivers - This sim would never have thought that rivers in Britechester could have sharks in it. They'll definitely think twice about swimming there again...
-Fear of Academic Failure - Bad grades lead to bad things like no degree, repeating courses, disappointing sims, and having money go to waste. These sims have that in the back of their mind, which means that they'll need to study more to get a good grade.
-Fear of Robots - After being zapped by a Servo or witnessing a Servo plotting a takeover, these sims will stay far away from any robots.
Tiny Living Stuff:
-Fear of Murphy Beds - After experiencing a murphy bed malfunction painfully, they'll avoid any murphy bed at all costs, even the fully upgraded safe ones. They kill sims after all!
-Fear of Flies - After being swarmed by flies, these sims will avoid them at all costs. It really feels like they could lead to death...
-Fear of Polluting - These sims have experienced first-hand what it feels like to be in an industrial neighborhood: acid rains, more fires, dirty air... They will try their best to avoid polluting and will feel tense if their lot contributes a lot towards industrial eco footprint.
-Fear of Vending Machines - After being crushed by a vending machine, these sims will rather buy their stuff from a sim or online.
-Fear of Slopes - After falling too many times, these sims dread the slopes. It hurts!
-Fear of Hiking in Mt. Komorebi - After being harmed by wildlife, these sims will avoid hiking. They will never join any hiking groups.
-Fear of Rabbits - After being attacked by a vicious rabbits, a sight of a rabbit will make the sim run.
-Fear of Chickens - After being attacked by a chicken, these sims will be the worst chicken carers.
-Fear of Foxes - This sim has lost a beloved animal to a fox attack. They will always be on the edge on lots that are known to be visited by foxes and will always shoo them away.
-Fear of Werewolves - These sims were terrified badly by a werewolf. Due to this, they'll run away from non-rampaging werewolves in their wolf form, don't like any howls, and werewolf diplomacy won't work so easily on them. Werewolf allies won't get this fear.
-Fear of Full Moon - This sim has experienced the horrors of the full moon. They will be afraid to go outdoors, wake up easier, and will be less successful during a full moon and will relate to werewolves by dreading the full moon when it comes tomorrow.
And to conclude, I'll present two trait ideas.
Coward - These sims are scared by littlest things and are more likely to develop fears of dangers (like fear of fire).
Worrywart - These sims become tense often and are more likely to develop fears from insecurity (like fear of failure).