It's not the first time that happened, but for example yesterday I answered a question. It was accepted with 3 upvotes. Someone ask to get some explanation so he can learn from it. I edit my post and gave an explanation. Since I edited my post I got a downvote with no explanation.
Is this the right way to encourage people to share knowledge?
What can Stack Overflow do to prevent such things, or force people to explain why they downvote?
It's very discouraging.
Edit: As referred to in an answer or in a comment I have misunderstood the downvote and a removed vote by a user.
So the interesting discussion in Encouraging people to explain down-votes.