Others have [answered][1] regarding downvotes, but here is my suggestion.

> Consider giving explanations when downvoting questions and/or answers. Knowing the problem with their contribution will help them rectify the problem and/or make better contributions in the future.

Of course this does not necessitate commenting, but leaves it to the discretion of the possible downvoter. 


  [1]: https://meta.stackexchange.com/a/313207/180367