It is without a doubt incredibly, terribly sad. But once I spent enough time thinking about it, it made me admire Cale so, so much. (Forgive for going on this tangent because I have spent a LOT of time thinking about it all.)
Because all that repressed trauma, unhealthy coping mechanisms and desperate denial aside... he is actually an extremely well-adjusted adult considering his circumstances.
Just look at the evidence.
Point 1: Cale is still capable of making friends, despite the fact that he was never allowed to KEEP them. As in, the curse took away ALL HIS FRIENDS no matter what he did. And yet! He has no "I must push them away by acting like a jerk (in order to protect both myself and them)" attitude like we see in most characters with this type of tragic backstory. Cale might "think" he is a jerk and a rude person, but he's actually just extremely straight-forward – when he bothers to have honest interactions with no hidden intentions, that is. Let's look at his first interactions with Choi Han as a baseline. He meets a guy whom he is scared of, he has every reason to avoid, and even has a lot to loose by helping him (aka. "ruining" the original plot of The Birth of a Hero). What does Cale do? Talks casually with him, ("Are you hungry?"), has him stay the night (which was EXTREMELY unnecessary, he could have just lead him to an inn and call it a day), refuses any sort of re-payment (reasoning he wouldn't use Choi Han out of fear of him, but he clearly has no issue of doing that later; the truth is Cale just likes him too much to take advantage of him in his weakest moment), and on top of it all, once he DOES decide to involve him due to change of plans? Cale gives him careful instructions, equipment, and treats him like an equal.
This is a pattern Cale has with everyone he meets later, as long as he likes and sympathises with them. He identifies their initial needs, provides them, gives advice, and brings them in to help out later. This is not the behaviour of someone manipulative.... No, it's the actions of someone with highly developed networking skills. And it makes sense! Cale spent the past 10 years as Team Leader, so he has experience. But notice, he's in a whole new life now; if he hated doing this, he would have stopped the moment he transmigrated. The same way he stopped working out and settled on getting Ancient Powers to protect himself, instead of continuing to keep a strong & fit body. Making friends this way is completely natural to Cale, to the point that he doesn't even notice he's doing this.
And considering Cale's traumatic backstory of constantly losing friends? This ability is downright miraculous for him to have. It can't be simply an acquired skill; it must come straight from his heart.
Point 2: Despite abusing his body to the limit during crisis, he is aware that rest is important and he strives to achieve work-life balance. It might sound ironic considering his track record, but it's true! He really tries!! It's not just his dreams of slacking, it's about how he tries to remind everyone to eat well during wartime ("Your Highness, can you at least make sure your soldiers can eat?"), the way he keeps collecting vacation homes in different places, how often he thinks of the "after" and his peaceful future with his family, the way he prioritizes food in any given situation (during shopping spree in Caro Kingdom, the only thing Cale bought for himself was a chicken skewer), the way he stated that as a Team Leader he initially used to work non-stop but gradually learned to occasionally take days off (he overworked himself overall, but it still counts!), and every other moment where Cale COULD fall into a stress-induced workaholic frenzy... but instead, Cale keeps trying to take breaks. It's his unfortunate circumstances that force him to risk his life over and over, NOT Cale himself. That is INCREDIBLY important, because all his previous experiences COULD have made him a completely stubborn working machine with a motto like "sleep is for the weak"!
It's not that Cale doesn't want to rest; he does! It's those stupid villains constantly threatening his homeland that don't let him do so!! His biggest ambition right now is become a FARMER for crying out loud!!! He could have been so much worse at this.
Point 3: He learned to forgive himself, instead of forcefully holding onto and internalizing survivor's guilt. He might have started off blaming himself for everything that went wrong, and his Failure Test in the Temple of the Sealed God shows that he internalizes all his previous his failures to this day... But if you read the story from the start, you begin to notice his character development in that area. It is, in its core, a story of a man helping others to heal, and learning how to heal himself. By the end of Part 1 this man, this traumatized, contradictory, wonderful man, states to others that "He finally started to consider his own life a little bit precious." That's so powerful!! Despite all of his circumstances TRYING to warm him into a miserable wreck, from his childhood to adolescence to desperate survival as an adult, he somehow STILL manages to re-learn how to cherish his own life!!
Cale initally started off as someone fighting to survive. Now, with his family by his side, he became someone who is trying to live.
And finally, Point 4: He stand in direct contrast to the White Star, who chose a life of misfortune for entirely selfish reasons, as someone who chose to live despite misfortune, for entirely selfless reasons. Cale could have easily become suicidal with the curse; in fact, it's kind of designed this way. Sheritt chose to create this curse specifically to make a traitor to her children suffer endlessly without the possibility of the release of death. The White Star was MEANT to regret what he did. By all accounts, Kim Rok Soo SHOULD have become suicidal. But... he did not. He was miserable, perhaps he lived with subconcious conviction that he would never live long enough to actually retire... but he still put all his efforts into survival. After losing Lee Soo Hyuk and Choi Jung Soo, he could have just quit trying. But that would be a disgrace to the memory of their sacrifice, wouldn't it? So he never let himself go that route. He trained his body well despite his deep dislike of physical exercise, learned to take breaks from work to keep himself functional, and became a hella talented strategist just to make sure EVERYONE under his watch survived, himself included. He kept distance from his co-workers, but not by cruelty; only by not spending any quality time with them and taking over their jobs, all to make sure everyone working for him was well and happy.
Looking at what and who Cale became, despite the curse and his apparent subconscious awareness of what it does...
It proves that no matter the circumstances, the core of his personality remained unchanged: a deeply caring, thoughtful, intelligent individual, with unquenchable desire to live his life to its fullest with everybody else happy alongside him.
And that? That is more impressive than any firework shower or clever scheme Cale has ever managed to pull off. Don't ever underestimate how much strength it takes to become someone like that.
