[glaak]

"Say I was asked 30 questions; I missed 3 of them and didn't get hired. It's a reasonable to assume that these 3 questions were considered important in the general assessment."

That would be true if those answers were assess on a strictly correct / incorrect basis AND those were the only things you were assessed on. Neither of those are true though in this case.

It's very possible that the questions where you didn't get an optimal answer you actually did very well on. And that there are other questions where you got the optimal answer, but it took you too long or you made too many mistakes in coding. Or you just came off as arrogant. Who knows?

I've seen many many candidates make similar assumptions to yours -- thinking they bombed specific interviews, when in fact they did very well on those. You might be correct about why you got rejected. But it's even more likely that you're wrong.

But this is absolutely true: getting the optimal solution in all interviews is not a necessary and sufficient condition.