The thing about Josuke is that, since the age of four, he’s had 24/7 access to a secret superpower that lets him instantly and completely fix anything that goes wrong in his life. Anything that breaks, anyone that gets hurt, anything that happens and has a negative result can be immediately rewound and brushed off as if it never happened with nobody ever the wiser; after all, it’s not like anyone he’s met can even SEE his stand, let alone realize he’s using it to do anything. Even if he does it while someone else is present, would they really believe that Josuke has some sort of healing superpower over the idea that they were just wrong about the thing having been broken in the first place? Probably not.
What kind of effect would that power have on a developing kid?
Imagine that he’s playing a video game and he’s getting really frustrated because he keeps dying in the same place over and over. If that happened to you, what would you do? Maybe gear up to chuck the controller into the TV? But, wait, you can’t do that! If you did, it might be satisfying for a second, but then you’d have to deal with the fallout of a broken TV and an angry parent. Not worth it. Josuke, on the other hand? If HE totally destroyed the TV, he could have that momentary satisfaction of letting the frustration out, then just quickly fix the TV and get back to the grind. No harm, no foul, no bits of glass to sweep out of the carpet or mother tearing her hair out in upset. Of COURSE he’d do it. Why wouldn’t he?
Imagine that he forgets his locker combination, because oops head too full of teenage miscellany. Would he go through the effort of fumbling around to find whichever pocket he shoved the slip of paper with his combination in to open it while he’s already late to class? Or would he just tear the door off its hinges, retrieve his stuff, and shove it back on in two seconds flat? Imagine that he’s messing around with some friends trying to climb a huge tree, when one of them falls getting two broken bones and a concussion. Would he call the friend an ambulance and decide climbing tall trees is too dangerous? Or would he just climb down, heal the friend back up, say something to the effect of “oh wow, good thing you ended up okay!”, and continue doing what he was doing safe in the knowledge that his stand could save him or cushion the fall if HE ever slipped? (He may not be able to HEAL himself, but he can certainly protect himself from the same kinds of damage other people get.)
Those are all just hypotheticals, but we do see examples of him doing those kinds of things in the series. He beats up anyone who pisses him off only to instantly heal them afterwards. He tears off Hazamada’s locker door to look inside without a second thought. In the wake of his grandpa’s murder, he destroys and fixes a ton of furniture in his house. He mentions fixing a friend’s broken leg. He DEFINITELY doesn’t shy away from anything dangerous, and not just out of general shounen recklessness. When Aqua Necklace hides inside his mother’s body, he forgoes any convoluted plan to save her and just punches her through the stomach without hesitation because he knows with 100% certainty, the certainty of lived experience, that she’d be completely fine afterwards, that she wouldn’t even notice. He waited to try healing his grandpa when he saw him sprawled across the floor because he didn’t have a doubt in his mind that, even if he took his time getting there, as soon as he did he’d be up again like nothing happened. (He was only wrong once.)
The thing about Josuke is that, since the age of four, he’s learned that being reckless almost never leads to consequences. He’s learned that its okay to make mistakes because pretty much any mistake he makes can be quickly and easily fixed with no lasting damage. He’s learned that, as long as he’s the one who takes responsibility for something, everything turns out okay for everyone.
We can see all that easily in his personality and the way he acts. He’s unbelievably chill, cool-headed and reasonable even in situations where NOBODY would be; stakes are very different for somebody who can effortlessly reverse anything short of death, so of course he doesn’t panic at those sorts of things. By contrast, things like “no money” or “waded into leech pool” (or, for a more serious example that comes up in the series, “friend/family is missing”) are not as easily fixed and thus are a much bigger deal.
Despite how much it takes to make him full on panic, though, he is far from careful on a regular day. Sure, he may be chill, but all that means is that he’ll calmly and deliberately do something insane instead of doing it in a panicked frenzy. We see dozens of examples of Josuke casually thinking his way out of situations by coming up with a crazy reckless solution on the spot that would be a last-ditch measure by anyone else, just because he’s so used to thinking with his stand’s ability in mind. (While you could maybe argue this applies to most Jojo protagonists, I still think Josuke manages to be one of the most reckless on-the-spot planners in the series while also being one of the most generally well-collected AND having a solidly in-place sense of self preservation, which is still an interesting combination in contrast with the other protagonists.)
It’s worth noting, of course, that Josuke DOES have a bit of a (literal) hair-trigger temper, but rages on Josuke are short, concentrated, and in a strange sense, controlled. While he’s certainly much less reasonable and more destructive than usual when in rage mode, said destruction never extends past the source of the anger; he feels mad, so he lets it out, handles the situation, and almost instantly falls back to baseline. Like chucking a controller at a TV and fixing it back up. A controlled explosion.
All of this is to say that, even when Josuke does reckless or destructive things, it’s not because Josuke himself is a reckless or destructive person; far from it. Josuke’s top priority is keeping the peace. Why else would he choose to be so meek towards bullies on the first day of school, even knowing he could wipe the floor with them? Why else would his first reaction to being told he was the result of an affair be to humbly apologize for the trouble his existence caused, instead of any kind of personal confusion or upset? The only reason he acts how he does is because he knows from experience that inserting himself into a situation, striking fast and hard however is appropriate, then fixing up the aftermath, is the most efficient way to solve problems for himself and everyone around him. He’s not a pushover. He’ll stand up for himself and what’s important to him when he needs to. But ultimately he just wants the best for everyone, and since he’s been gifted the ability to fix things, to heal, doesn’t it make sense to use it?
In that way, Josuke acts as a perfect foil to Kira. Neither of them deny themselves whatever they want, neither of them are used to experiencing consequences for their actions, and both of them just want a peaceful life; the difference is, Kira destroys problems. Josuke fixes them.
An interesting side effect of this mindset is that Josuke ends up taking on responsibility for all sorts of things that are in no way his burdens to bear. We see a number of times throughout the series that he never backs away from a situation he could potentially do something about, to the point of even inserting himself into situations he really doesn’t need to. Any time he CAN heal someone, he does; in the Harvest episode, in particular, Josuke heals a number of tiny injuries Okuyasu picked up without comment as soon as he could. It’s so ingrained that, during their dice game, Rohan mutilates himself in order to keep Josuke from running away, since he knew Josuke would never leave him like that even though they hate each other. Of course Josuke would consider it his responsibility to heal the hand Rohan messed up himself such that he’d stay in a terrible situation he could easily walk away from just for the opportunity to heal him. It’s a no-brainer.
And because Josuke takes on so much extra responsibility, because Josuke is considered by both all his friends and himself to be the multi-purpose get out of jail free card, he takes it that much harder whenever anything seriously goes wrong. There’s almost a level of existential disbelief to it. Sure, anybody would be upset when something bad happens, like, say, a family member or friend dying because of your own negligence, but with Josuke… When his grandpa dies, and then paralleled later when Okuyasu gets blown up by Killer Queen, he sounds confused. Like he just experienced something impossible. People can’t die around him. It’s not even a question. He has a healing superpower! People can’t die around someone with a healing superpower, especially not when they’re literally a few steps away!! So, then, if it really did happen, what does that say about him? When he gets the call from Koichi during the fight against Sheer Heart Attack, he panics and rushes into action immediately. It’s easy to imagine what could have been flashing through his mind.
Because of his stand, the stand he got after a formative experience when he was just a small kid, he always has the unique ability to help. To help himself, to help others. All he has to do is put in the effort, show as much kindness as he can as soon as it’s needed, and he can keep everyone happy and healthy. At the end of the day, if he can do something, he will. Every time.
The thing about Josuke is that, since the age of four, he decided that he wanted to be like the person who saved him when he and his mom were stranded in the snow. He saw the way that guy went out of his way to help a total stranger, showing kindness to people who needed it more than he could ever know, taking off his coat in the cold despite his own injuries just because it was the right thing to do, and he thought: “I want to be like that”. Through that decision, he received the power to do just that. Over the years, he used that power again and again; for himself, for others, for everyone he could. And eventually, that’s exactly the kind of person he grew into.