Chuck and Jimmy's Dad

Don't ask such questions, that's how we get a prequel spin-off to Better Call Saul about his parents. That'd just be too much.

It definitely seems to be a factor in Jimmy turning to the dark side. He saw what being a nice guy gets you: NUTHIN.
He still had a lot of goodness in him, taking care of Chuck all those years, but Chuck squashed that out of him and what remains is Saul. reverting back to Slippin Jimmy to get the music store douches to pay what they promised. They were going to screw him (after his free ad DID bring in more customers than ever, so he really DID provide them a valuable service). The overseer guy at community service was a giant dick as well, so at the moment he's only using his dark powers for justice.

I think it was Jimmy who was the influence. Chuck saw Jimmy taking advantage of people and getting away with it. Then when he did it to their dad, Chuck blamed Jimmy for wrecking the business and causing their dad to die. That's why Chuck did a lot early on to sabotage Jimmy's career- he was not going to let Jimmy wreck the law firm by taking advantage of the customers.

When Jimmy used Chuck's affliction against him, and particularly the conversation on the phone where Jimmy tells him he will die alone, Chuck sees himself going down the same path as his father, where (at least in his mind) his weakness can be exploited by Jimmy at any time. And it's the main reason why he is taking steps to cure himself.

I really liked that scene with the story about the coins (I think BCS has some terrific writing that makes these relationships far more nuanced than most other shows). Here, a childhood story illustrates the moral direction both Jimmy and Chuck would head towards.

Jimmy wants immediate results and wouldn't mind using a scam or two to get it. Chuck would've sided with the father and would see his "soft touch" as unbending honor and genuine goodness. But an earlier story that Chuck shared shows that the father seemed aloof to Chuck, and both parents favored little Jimmy more, and that's where the resentment started to brew. To side with the father respect the values of honest hard work, decency, truthfulness and loyalty - only to still be passed over....has to wound Chuck deeply. In a world of structured law and certainties, his lack of affection from his parents (at least, compared to what Jimmy was given) is one thing that does not make any sense to Chuck's ordered life. The scammer, liar and troublemaker gets more parental love than him. For what? Being the baby brother? Making people laugh more?

But to get back to the main thread - we're getting some interesting past history with these characters and a better understanding on how Jimmy acquired his worldview.