Marinette Dupain-Cheng's FUCKING problem is. Well honestly it's the PTSD. This girl has mountain of trauma from the whole superhero stuff + years of school bullying beforehand (because yes, school bullying is a lot less impressive than life-or-death situations, but years of debilitating social isolation and harassment does in fact have serious consequences on folks growing up) which she copes with by being an absolute control freak and copes very badly with said control getting out of her graps. But her SECOND fucking problem is that the girlie has no mentor figure in her life.
In season 1 of Miraculous Ladybug, Tikki seems to be the one taking up that role. Makes sense, right? Tikki is a thousand years-old eldritch abomination in the shape of a huggable plushie. Surely she's wise beyond her years, surely whatever course of action she advises Marinette must be the best!
Except no, it's not, because Tikki is not a human and therefore only has a vague sense of morality. She only ever gives Marinette the most generic of advice- don't lie, don't steal, that sort of things. For any sort of gray situation, Tikki got fuck-all.
For season 2-3, Master Fu takes on that role- he's a century-old man, last of the order of the guardians, the one who knows the most about all Miraculous things. Surely he has the wisdom necessary to go forward!
Except, still no. Fu only knows the most basic of things because he nenver completed his training. He's winging it and pretending to know more than he does cuz these kids need guidance, but he is as lost as they are on that one- and once he's lost his memories, he is completely written off as a viable mentor.
So, who's left? Su-Han? Dude is still stuck centuries in the past. Bunnyx? She refuses to say anything substancial so as to not interfere with the time stream. Nathalie? Working with Gabriel is proof enough of her lack of judgement.
Marinette wants to do good. She wants to do good so, so bad. That's why she keeps asking people did I do the right thing? Was I right to lie?. What she wants isn't so much validation for her actions as she wants someone, anyone to tell her what to fucking do. It's fine if she's told she did a bad job- she just wants someone to tell her the objective truth. But the kwamis refuse to answer, and Bunnyx refuses to answer, and anyone left are people Marinette sees as peers rather than mentor figures (i.e Kagami & Nathalie) so their opinion has much less weight to her. And that's why the girlie is getting insanely fucked up over her own actions. It'd be fine if someone validated her. It'd be fine if someone condemned her. But it's a decision she picked on her own and no one but herself can judge, and it's driving her insane.