Joanna Chambers' M/M "A Christmas Carol"-tribute, Humbug, does many things very well. One is that she doesn't utterly rehaul Scrooge's personality.
Dickens does a fine job preparing us for the final transformation by indicating that Scrooge was a lonely boy who became a sensible if workaholic young man who had the chance to marry the love of his life. He was, once upon a time, a friendly, sweet-natured guy, who turned into a "scrooge" due to his own choices and the bitterness of life.
Okay. But the end does leave one pondering whether the bitterness of life can be wiped out in one night. Where exactly does personality come from if not one's choices and the exigencies of life? Can a person utterly undo what has made him or her in one fell swoop?
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Problem: the gig isn't totally in line with his personality, so he becomes--as characters in the story repeatedly tell him--a "dick." He later tells Rob, the Bob Crachit character, "I think [this job] brings out the worst in me." Instead of becoming the kind of leader whose team is the best because they admire him and feel appreciated, he becomes (is becoming) the kind of leader who wrings work out of people through unreasonable demands and sheer sarky irritation. He is acting in accordance with what he believes to be the "role" of manager--and he does it well, but it makes him absolutely unpleasant to be around.
After his epiphany, he returns to his first plan to be a math teacher. And here is where Joanna Chambers really knocks the characterization out of the park: because of course, Quin has to be the BEST teacher. Only this time, what he wants and what he brings to the table are in line. He'll get in his students' faces ("They'll love you," Rob says, "because you're sarky"). He'll get in their parents' faces. He'll tick off the school board but still win. The aggressive energy that makes him unlikable in one field (that he doesn't feel at home in) will make him an excellent advocate in another.
As in the original tale, the main character's epiphany rests on an acknowledgement of his own failings, in this case through a forced cell-
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Quin is a Scrooge whose tweaks to his life believably result in a much, much happier life in the long-run.
As Bruce Willis proclaims in The Kid after seeing his contented 80-year-old self: "Look at us go. I am not a loser!"