Ask HN: Stupid Question – How to undo accidental upvote/downvote?

It's such a basic thing, but I'm not sure how to do that on HN. Call it old age, but sometimes I accidentally click upvote when I had to click downvote and vice versa. How can I undo that? It hides both the icons as soon as I click on any of them, and I don't want people to feel bad about my mistake (And there are studies which show downvotes affect more downvotes)

Edit: There might be some answers saying the Karma points don't matter. If that is the case, we should just remove the voting system altogether. It's more about not making the comment writer feel bad, than the Karma points (and I know you feel bad on downvotes).