It’s seriously annoying that so many opinions are about Walter White being that egotistical maniac who destroyed that wonderfully crafted criminal operation… Walter wanted to quit after his first stint, because of the consequences it had on his family — Skyler had just found out about his secret activity, their marriage was in jeopardy, and at this point he did place his family above all else. Then, Gustavo gave him his big motivational speech, “a man provides” and all that crap (with strategically placed toys to pretend he was himself a family man), because, as Gale had rightly guessed, he wanted the best possible chemist for this job, and Walter was it. Then, merely a few weeks later, because Jesse went after two scumbags who murdered a child, who happened to be low level drug dealers from Mr. Fring’s operation, and Walter killed those scumbags to save his partner’s life (out of sheer loyalty, at that point it wasn’t about manipulating him), Mr. Fring decides to get rid of them both. Does that make any sense ? Anyway, Walter’s survival instinct kicks in, he figures out that by killing Gale they both get to live, and it works. That was a last resort decision, he didn’t want any of this to happen in the first place. Then, shortly thereafter, Gustavo who was so adamant about getting Jesse killed, starts using him to eventually turn him against Walter, and it works. Walter understands that he’s going to be deemed expendable once again, and starts freaking out. Meanwhile his brother-in-law Hank is closing in on Gustavo’s operation, Walter interferes with his investigation as much as possible, both to prove his loyalty to Gustavo and to protect Hank himself, but the situation inevitably continues to escalate. After being threatened, himself and his whole family (the infamous “I will kill your infant daughter” speech), Walter first attempts to flee via the “vacuum cleaner guy”, and asks Saul to anonymously inform the DEA about a hit on Hank (again, because he cares about his family, despite everything he’s done up to that point he doesn’t want them to suffer — and in this particular case it’s not even a consequence of his actions, even if Walter hadn’t been involved in the methamphetamine trade, Hank would have been targeted for murder once he would have flown too close to the Sun). But the money is gone, fleeing is no longer an option, so he has to take matters into his own hands — that’s when he ends up blowing up Gustavo, and then the lab to cover his tracks. Again, he didn’t want any of that shit in the first place, if he hadn’t been threatened over and over for no sensible reason he would have “done his job, known his place”, none of this would have happened.