He had the rare gift of analytical intelligence and creativity. True geniuses usually have both. The rest of us are lucky if we're adept at either. He could imagine scenarios and devise thought experiments better than most, but also had the rational aptitude to limit his imagination to things that might lead to something useful or novel.

Einstein had a famous quote that his thinking was often "muscular" rather than in words. He was intuitive in the way he thought about complicated problems. That's not to say that he also didn't work and study hard, but he clearly had some kind of advantage that is hard to understand.

I heard that his brain was wired differently than a normal brain. Not sure if that is the explanation for his genius, but it's a good start

He had differences more "convolutions" in the prefrontal cortex. This is important in abstract thinking.

Good article:
https://earthsky.org/human-world/einsteins-brain-was-different-from-other-peoples

There's quite a story behind what happened to his brain after he died. It was literally stolen by the doctor who performed the autopsy.

https://www.nationalgeographic.com/science/phenomena/2014/04/21/the-tragic-story-of-how-einsteins-brain-was-stolen-and-wasnt-even-special/

Maybe he just got lucky. Sometimes people are just in the right place at the right time.

That's a little nuts. He made like 3 or 4 major discoveries - each of which would have made him famous.

He didn't even win the Nobel Prize for relativity. He won it for the photoelectric effect.

He also have very devoted parents who nurtured his interest in science. Not the whole story of his genius, but it certainly helped

Some people are just smart. End of story.

Yeah, but you're not born knowing calculus and physics. Smarts help you acquire that knowledge but there are a long list of teachers, colleagues, etc who all contributed to Einstein's accomplishments either directly or indirectly.

He was actually not a particularly good student. Maybe he was a late bloomer.

There are rumors out there that Einstein was terrible at math and failed a math class in his early schooling days.

It's true he wasn't a great student, but it wasn't caused by a lack of smarts. He just didn't study very hard.

https://history.howstuffworks.com/history-vs-myth/did-einstein-really-fail-math.htm

Yeah, I'm sure he just stumbled across E=mc2 in a cracker jack box, or something. Come on dude.

Luck must have played a role. It's just hard to say how much.

If he had been born 50 years later, relativity (and the rest of it) would have already been discovered.

There are a lot of physicists today (some who are as smart as Einstein was) who are probably extremely jealous they weren't born when Albert was.

There is still a lot to be discovered.

Not many big discoveries lately - at least none that have made anyone a household name like Einstein.

Somebody is going to unify quantum mechanics and relativity and become as famous as Kim Kardashian (ok, well maybe not that famous)

Some people are just smart - that is all there is to it.

Smart is hard to define. You know it when you see it but it's hard to come up with a list of properties or attributes of "smarts".

Whatever it is, Einstein clearly had it, but he also had a curiosity about the world that distinguishes him from most people.

Agreed, curiosity is the bigger factor here.