I was at an academic conference earlier this month, and several of the speakers made affectionate jokes about one of the speakers - how he couldn't shut up, how he was impossibly argumentative, how he was terribly rude, and basically how he was a bit of a troll. And they were right, he was all those things, plus he looked a bit like a frog. Imagine a short frog with glasses, a thick Noo Yawk accent, and the social graces of a falling brick.
And yet he was such a persuasive and entertaining speaker than even when I thought he was dead wrong I wanted to hear more and find common ground with him. I liked him even when he was being an ass, and even in cases where I knew he was wrong (eg when he deliberately skipped over some significant issue because it undermined the argument he was making).
The things you mention help, but are by no means essential. You don't even need to believe in yourself, as long as you believe sufficiently in your idea.
And yet he was such a persuasive and entertaining speaker than even when I thought he was dead wrong I wanted to hear more and find common ground with him. I liked him even when he was being an ass, and even in cases where I knew he was wrong (eg when he deliberately skipped over some significant issue because it undermined the argument he was making).
The things you mention help, but are by no means essential. You don't even need to believe in yourself, as long as you believe sufficiently in your idea.