I have to comment on the subtle way TMBS uses Curtain’s father relationship with SQ to show the contrast between him and Curtain in the books.
I love the books and the tv show, and I think both sets of characters are fantastic. However, in some cases, they are different characters and Curtain is a great example (from a character writing standpoint and also literally, Nathaniel Benedict and his backstory with Nicholas are not in the books). But what really sells it for me is how Curtain treats his son in the few scenes we do see and the few things we know about their relationship.
1) Show Curtain actually adopts SQ. In the books he comes to care about him, but he would never take the step of openly considering him family, even though it would have almost guaranteed book SQ’s loyalty. This version of Curtain does adopt SQ despite his vulnerability trigger. (I won’t get too into my “Curtain/Garrison/Milligan/SQ’s dad were friends that fell apart theory” cause that’s a whole other thing but click here to start that rabbit hole).
2) Show Curtain doesn’t involve SQ in his work. Book Curtain uses SQ as an executive/messenger, puts him in the whisperer and repeatedly wipes his memory to keep him by his side. Show SQ was not an executive or messenger (in fact he has no idea what his dad does) and so far has shown no signs of being brain swept. Even in season 2, when Marlon asks if SQ can come back for the next stage and Curtain says no, we as the audience assume this implies SQ has already been given the “happiness” but what if Curtain’s refusal to bring SQ back was actually him preventing SQ from taking the artificial happiness? (They didn’t get the actor back so I guess we’ll never know).
3) Show Curtain encourages SQ’s artistic talent. I’ve seen a lot of fics where Curtain resents that SQ is artistic and wishes he were “smart”, but if you watch the show, Curtain doesn’t do that. He does art projects with his son, he has rules about him going to the forest to paint but he still lets him go, and when Garrison interrupts Curtain, he doesn’t snap at SQ to do his homework, he suggests his son sketch, an activity he knows SQ enjoys. It would be easy to have a scene of Curtain admonishing SQ for his grades or not appreciating his art, but instead the writers chose to put in scenes showing the opposite.
4) When Reynie gives Curtain a narcoleptic seizure in the season 1 finale, it’s SQ that really sets him off. At first Curtain tries to mock what Reynie says: “I don’t think I’m a bad person either who thinks that?/“ok this is embarrassing”, but once he mentions SQ, Curtain gets visibly uncomfortable like “oh he went there oh no” and goes “okay, that’s enough that’s enough”, and realizes that he is losing this fight.
5) Finally, yes, we do see that Curtain is a bad father to SQ. I’m not denying that. The man deserves to be nailed by a golf cart. But: the main times when we see Curtain being a bad parent have a pattern: they occur when SQ is in danger of discovering who Curtain really is. The first is when he asks to bring Reynie to the forest. Curtain panics, realizing Reynie might be working for Nicholas, and now he’s forming a friendship with his son. Telling SQ that Reynie is using him was cruel and SQ is clearly devastated. SQ shows an awareness that his father speaks to others that way (he sees how his father speaks to Garrison) but might not be used to his father speaking to him that way which is why he takes it so badly. Then there’s when Curtain interrogates SQ, asking if he took a friend to the forest/if Reynie is really his friend, and SQ throws back in his face the “right cause who’d be friends with me” line and openly lies to him. Book Curtain would have at least called him out, or much worse. Show Curtain doesn’t, even though he knows his son is lying. Whether it’s because he’s scared his son is turning against him or because he’s ashamed of what he said to SQ earlier (“how many friends have you had”?) or because he doesn't want his son to be more suspicious, we can only speculate. Finally, SQ confronts Curtain about the antennas after finding Reynie’s letter and refuses to tell his dad about his conversation with Reynie. At this point, Curtain doesn’t know how much his son knows or what he will do. He could brain-sweep him. He could yell and tell SQ to never disrespect him again. Instead, he handles it in kind of a weird way where he admits to being under stress and having clouded judgment (which is a very rare moment of vulnerability and emotional awareness not just from Curtain, but from any abusive parent) and asks his son to please leave, though rather forcefully. Obviously, comparing him to book Curtain puts the bar on the floor and show Curtain was still horrible and should have told the truth, but the other negative alternative ways to handle that situation (Book Curtain’s torture and brain sweeping) would have been so much worse.
One of the most interesting aspects is how Show Curtain compartmentalized his son and his work so much that they became totally separate and how little SQ knows since he’s not working as a messenger or executive. SQ, on his end, has likely seen the way his father treats others, but work stresses out a lot of people, some people are ruthless in their careers but are good parents, he probably wishes his dad was different so he could have friends (because every other kid at the institute has to be controlled by Curtain, or at least is striving to please him at all times, which prevents genuine friendships), but his dad never does those things to him or at least not to that extent. So as long as SQ never talks to his dad about work (in his mind: “because it stresses him out”), his dad will never treat him the way he treats everyone else and since SQ has never know anything else, life seems alright to him. It’s only when Reynie starts pointing out Curtain’s flaws that SQ questions him and starts to see that maybe there’s more going on.
This could also explain SQ’s season 2 absence. SQ was on the boat, he knows how his dad screwed Garrison over. His biological father used to work for his dad. And SQ will never know whether Curtain screwed his biological dad over like he did Garrison, because Curtain will never be vulnerable enough to tell him the truth. Meanwhile, Curtain also realizes that his son is now curious about his work, and keeping his double life and his son would involve going a step beyond lies/gaslighting and doing the things book Curtain did to his SQ and show Curtain so far has been unwilling to do that. So SQ now has a motivation to leave and Curtain has a motivation to let him go: SQ can’t trust his father after what Reynie told him/what he did to Garrison and the only way Curtain can make SQ stay is by forcing him or messing with his free will/memories and so far he has refused to do that, at least that we know of (granted Curtain could have also told SQ the truth and voluntarily changed his ways, but after lying for so long, SQ might have chosen to leave anyway).
