As a kid, he started to believe that everything is a scam, that the people who think there's more to life than a sequence of scams are either liars or suckers waiting to become targets for petty schemes.

That's Slippin' Jimmy. It wasn't about scamming "honest" people. It was about scamming anybody he could, just because he thought that's all that there was to life.

And eventually he wanted to prove -- most of all to himself -- that Chuck's great success in life was also fundamentally about finding the cracks in the system. So Jimmy wanted to show that he could scam his way to a legal career. And he basically did, but as we saw, just becoming a lawyer doesn't make him Charles McGill, and we all saw how that turned out.

So when Chuck died, he discovered that scamming people is NOT the purpose of life. But by then he didn't think he could be good at anything else. So this leads to the nihilistic Saul Goodman. Life is the process of getting from one day to the next, nothing more, and if you're skillful at dishonesty you can pass those days with more comfort.