One of the biggest things that ever seems to kill me when I’m doing well is just getting sloppy. I do something stupid and make a lot of small yet crucial mistakes that always wind up getting me killed.
How do people work on that? Is there some kind of strategy you employ to help keep on your toes and not slip into the trap of feeling like you can take on anything you come across? If there is I’d really like to hear about it. These silly deaths are just…silly.
Number one thing that helps me not be so complacent is safe mod combined with the [ ’ ] key. This lets me ignore stuff like dogs or rats in open daylight, but it lets me still stop for actual threats like Jabberwocks, Chicken Walkers, Wraiths, ect… Other than that, remember to bring disinfectant, a crowbar, a source of fire (preferably a refillable lighter), painkillers, a knife, some bottles, and a means to defend yourself that you can rely upon. Coffee, or another stimulant that you can get your hands on is a good idea too, for that extra combat edge.
when you finally find a gun ALWAYS bring it with you, along with the ammo. Sometimes, you accidentaly meet a hulk and can’t run anywhere so drop your melee weapon, equip the gun, shoot the thing to death, grab your melee weapon from ground and RUN before things get drawn to the noise.
I often run into the same problem. What I often do when that happens is shut down the game and come back to it fresh. When I’m being smart at least. The other option is to start pressing the keyboard buttons harder because everybody knows that a good hard push on the arrow keys will make your character faster and deal more damage.
Also, drinking and playing cata has has ended in a few good characters checked off the list. Don’t drink and cata. I also forget how squishy new characters can be sometimes, which leads to more new characters.
Planning.
Plan out what you are doing, why, and what you will need to protect against. You dont always need to be kitted out for hulk, but you should always carry a gun or two around. You should always carry a melee weapon, or something that can substituite for one (a bayonetted rifle or martial arts), and you should always consider carrying a grenade of some kind or some manhacks or something to distract an enemy.
Smoke grenades work really well, and an incendiary grenade will kill most things who arent immune. A car with active turrets covering you helps, and taking some basic stimulants and medications will help a lot too.
Its important to know what you have on you, what you have in your car, how quickly you can escape if things go wrong, and most importantly recognizing when something could go wrong and fleeing before it does. There is no pressure to kill everything, and if you run back to your motorbike to get a shotgun or back to your base to get that heavy power armor the monsters will be waiting for you still.
-Fourth, how well did you prepare yourself? Did you do the best job you could have? This step is the learning step.
Preparation is as always key; you need to balance out safety and task orientation. Every volume of space dedicated to your protection is a volume not used for whatever task you’re doing. Whether you are collecting rocks for a fireplace or looting a grocery store, you need to find the compromise between security and task. You need to also decide between storage, mobility, and protection. Before going out it’s always a good idea to consider all the possibilities and the likelihood or inevitability of their occurrence. And you need to take proper precautions for them.
Sometimes an item isn’t going to be needed immediately in the field. So it’s safe to leave it at your base, stash-spot, or in the back of the car. Some items should be carried in the front seat of the car or even in the driver’s seat for easy access. They need to be available and easily found if needed, but take up too much space if always carried on you. And some items deserve a permanent spot in your inventory. Items such as a knife, a means of fire, a weapon of your choice skill, and a ‘hulkbuster’ need to always be present. Alcoholics should prepare alcohol for regular use; and other addicts need to prepare rations of their vice. Carrying healing supplies and choice stimulants should also take a priority.
Your Mother only exists in your dreams; you need to take matter into your own hands.
I always carry multiple stimulants/painpills for emergency escapes. Combined with the run key ". Also once I’ve raided a lab I always keep a teleporter on me for any last chance dances.
I’d have to agree with saving and coming back later and planning. If you save in a safe area, come back, and have a well rounded plan of what you’ll need to do next, it tends to make me avoid stupid mistakes. It’s a turn game too, if things look particularly sticky walk away from the computer for a minute and smoke a cigarette or eat a snack or something. Sometimes it can save you! Other times it won’t. 
A Fragile character also tends to make me play MUCH more conservatively.
Make an escape plan!
-2 molotovs
-Adrenaline injector
-Methacola
Simply consume in that order and start running. Satisfaction guaranteed!!
As others pointed out, careful preparation is the key to survival. In addition to what was already mentioned above, I’d suggest to always keep some alcohol on person, especially if you rely on melee (and to a certain extent, every character has to rely on melee). A quick swig of beer or any other alcohol gives you a slight boost in strenght, which can be handy in certain situations. I’d suggest to use a hip flask filled with strong alcohol, as that solution is both light on encumberance/storage but still gives you multiple uses of alcohol. But as in real life: don’t overdo!
The next thing I’d suggest is simple redundancy. ALWAYS keep a spare of whatever you need. There are zombies which can disarm you, your ammo can run out, weapons can get stuck in opponents. If such a thing happens, it’s always good if you have some backup weapon, some spare magazines or other means to defend yourself.
I currently run around with a bow as my main, a taurus pro .38 in a fast draw holster, a tanto in a sheath, and a steak knife in a boot. As well as ALWAYS carrying a pair of earplugs, and 5 bandages with me. While wearing a filter-mask and a knit scarf, along with lots of survivor equipment.
Meanwhile my apocalypse RV has a console(trunk) full of loaded guns, spare loaded clips, and spare ammo that doesn’t have any extra clips to go into. The trunk behind the driver’s seat has all the guns/ammo missing their counterpart that I might find at some point, and the floor trunk walkway space diagonal from driver’s seat has clothing that I might feel the need to change into.
I plan to replace the boards with stow-boards (at least near the driver’s door) so that I can put things like snacks and emergency meds closer to me while on the road.
I have spent most of this game near base building up my RV, moving supplies and general getting a wide range of skills high. zombies are still low level, so Im going to tweak the evo rate that I clearly set lower than I should have.
In relatively recent experimentals, an awl pike makes a surprisingly effective safety blanket. Being able to melee something two tiles away is incredibly useful, since for most enemies that’ll translate into two free hits before they can retaliate. Bayonets are a lot more useful now that switching weapons actually takes time, since you might not always have time to pull a pike out of your back pocket.
Oh, dynamite is also a relatively easy to make equalizer with abundant, easy to acquire ingredients. Just make sure you can get out of the blast before your target does, or wear something like plate armor. And don’t use it indoors.
Edit: Basically, my way of dealing with overconfidence is to make sure that confidence is justified. Feeling like I can take on anything is not a liability if it’s true. 
Maybe you just need harder monsters to fight.
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<.<
Try my mod