I have asked a low quality question or one that has an obvious answer or an otherwise question likely to be downvoted. These you should delete if the question itself is bad not about it being worded wrong. Sometimes there are questions that get downvotes even though they are not obviously bad. As soon as I get a score of -1, is it a good idea to delete the question? If deleting it at -1 is a bad idea, at how many downvotes should I think about deleting it?
It's a good idea to delete a question or answer as soon as you realize that it has no purpose, will never do you or anyone else a bit of good, and nothing you can realistically imagine doing to it will change that fact.
But one downvote? That's nothing. Scratch that; it's better than nothing, it's a challenge - someone's told you you don't got what it takes, you gonna take that from 'em? You gonna take crap from An Internet?!! Hell no! You're gonna show 'em! You're gonna re-read the question, think about it hard, practice that empathy and imagine what it looks like to someone who isn't you... Then you're gonna edit the crap out of that post! You're gonna make it look so good, the person who downvoted is gonna look like an idiot. Folks are gonna wander by & see it & think, "what a fool that voter is, voting in the wrong direction - let's all laugh at them, and then upvote this".
And you're just gonna sit there, smirking like the cat who got the cream.