What was Walt's worst, most critical mistake? MAJOR SPOILER ALERT

These are very good picks. I don't know why the hell he would keep something around like the Leaves of Grass anyway.

You've got good picks. I'll try to keep this SPOILER light, but yeah, finish watching before reading.

My number one agrees with your stating that he turned down Elliot and Gretchen, yes. But in his operations...

I'd go with your number three there. If Walt could've checked his ego and let Hank think Gale was Heisenberg, Hank would've let leads go cold for awhile.

Now, if Walt was still going to cook, the Blue would still turn up and Hank would probably have come back around at some point, but who knows what could've happened there?

He makes a MAJOR mistake involving a GPS later, but things are already pretty much spiralling out of control.

My number two choice of mistake he makes is in the final season when he starts to try to build his empire. He could have taken a buyout and ghosted, but he doesn't, and that leads him to hiring on questionable people (because he doesn't have Gus' networks or business sense) and getting in bed with some real shady types. All of that leads him down the real darkness.

Number three: he was "out" and let Gus talk him back in to coming on board for more cooks.

I don't really agree with your number one choice, mostly because "get rid of that evidence" is a reasonable goal and anticipating the fallout was impossible. In other words: that's more bad luck than a mistake.

All points where Walt doubles-down and accelerates his dark fate are due to his ego. His problem is pride. Vanity causes Walt to tell Hank - I don't buy that he's that drunk. He hates somebody else getting the credit. Look how he reacts to Jesse cooking his formula. It's also pure vanity that makes him try to recklessly build an Empire with Jack and Lydia. And, of course, his delusions of grandeur make him come back on-board with Gus.

There's a moment in the final episode that really puts Walt's perpetual ego trip into perspective - a scene between Walt and Skyler - and I'd love to hear your thoughts on that once you've seen it.

His least critical mistake was carrying the barrel.
It's a barrel. It rolls.

I think it's close between 2 and 3, but closer to #3. As another poster adequately stated,

His problem is pride. Vanity causes Walt to tell Hank - I don't buy that he's that drunk. He hates somebody else getting the credit.

I'll say when he had a chance to sell those chemicals from the train heist for $5 million and kept going was the straw.

He already had millions, but then to turn down that additional $5 million and keep going was simple greed. He had no idea how much money he had already made - Skylar showed him the storage unit and neither of them knew how much it was but it was $80 million.

He could have then moved that family away from ALB for good. Why on earth they stuck around that town I'll never know. They could have started fresh away from the bad people, away from the DEA, and Marie. They would have been safe.

Not killing Jesse in the Confessions episode when he had the chance.

Turning down Elliot and Gretchen is the only correct answer :p

As I recall Walt got the idea for cooking meth during a ride-along with Hank --- NOW can't remember if that was before or after his diagnosis of cancer

AFTER the diagnosis he determines that he doesn't have enough insurance to insure a good enough life for his wife and son, AND it was possible to do so by cooking meth

So he teams up with Jesse and starts cooking and putting the cash aside, and had a million or so in the wall

THEN his cancer went into remission totally --- He'd made all he wanted to -- he could have stopped and gone back to his life

But NOOOOoooooo he continued cooking

That was the worst decision and where he Broke Bad