Why did Tony Stark fail to make Ultron but suddenly he could fix the time travel in Endgame so easily??

Bruce and Tony clearly did not understand the stone they were working with. He had a lot of time to grow. He developed as characters do. He was just as surprised as you when he did it.

And some would say he was too successful. He wanted to defend the earth with Ultron, and Ultron tried to do exactly that. Did Tony agree with the methods? No. But would his plan have helped the planet itself? Yes of course.

Oh give the guy a break, he only created a reactor in a cave, synthesized a new element on the periodic table and figured out the time travel equation...so he fail creating a world protecting A.I., big whoop ..nobody’s perfect 🤷‍♂️

Maybe making an AI that does exactly what you want is even harder than traveling through time.

I mean he didn't really "fail" with Ultron, it's just that the robot developed too fast, too much all at once, and that caused it to become the way it was

Wasn't it implied that he'd been messing with time travel for years?

Pretty easy. One involved an infinity stone and one didn't. Ultron's intelligence came from the mind stone and there's no way Tony would've known Ultron would turn out that way. Matters of mind and soul are more Dr. Strange's realm. Time travel is just manipulating Pym's technology.

To be fair he succeeds on the A.I front with Vision...

So he’s made non murderous A.I as well

He didn't fail.

The stone was constantly messing with the interface and stuff

Then stone created Ultron

@grinningf0x: he really didn't, he just tried putting Jarvis in visions body, and when it was finishing, thor messed with it, and they say it was a mix odd Ultron, Jarvis, and whatever thor added

He didn't fail the AI was too advanced he should have dumbed it down.

Here's the thing y'all are forgetting. He didn't figure out time travel on his own. Without Ant-Man, he wouldn't have a large portion of the work already done for him.

Why do people bring up creating a new element as something only Tony could do. Real humans have created like 25 man made elements on the Periodic Table. Compared to time travel and created real sentient AI, Its one of his weakest feats to be honest. "Congratulations sir, you've just created a new element". Yea, so did 25 other dudes :/

Cause you normally get smarter as time passes.

@rdskns4eva: 25 dudes out of, like, 7,000,000,000....

His mind was influenced by Scarlet Witch.

Because the plot said so.

More like, 25 out of how many people are actively trying to create an element or mistakenly created an element. Im not sure what that number is but it at 7 bil.