I think that the main reason for a downvote is to convey that a post is not up to the mark, or does not show proper effort on behalf of the person who posted it. In other words, a downvoted post has to be improved.
[Note that I'm not saying this out of any dislike for downvotes, but as a means to improve (in my opinion, you are free to object) the way the users can work.]
Now, I just thought that it would be nice to include a suggestion box (or one similar to the "reason for edit" box) where users can, retaining their anonymity, suggest with a limited number of characters, any improvement that the user who answered can make to improve the overall post, while downvoting.
It need not even be mandatory but can help users who keep getting downvotes without actually realizing why, and also fail to improve.
Once again, please note that this is not because I have been downvoted without reason. For, instance, one of my answers about Bernoulli's theorem was downvoted, and it was plain awful (the answer, not the downvotes), fully deserving of the downvotes. It was a poorly constructed and fundamentally wrong answer (thinking back about it), that can become an example of how answers must not be.
But I have also had an answer (which I admit was not great, but I cannot see how to improve it) which was downvoted (This is not a rant, please). The answer did not deserve an upvote, I can say that, and downvotes hardly change reputation, but I wished a feedback (just a phrase, like," lacks clarity") would have been of great help in improving myself.
But I just thought If users get feedback on why their answers were downvoted, won't it be better for the users of the site?
(I don't really think you need to say why you upvoted an answer, so that feels a bit rudimentary to add)
These are just my opinions. I would like to know if it is worth.