Posting about someone instead of talking to them is just yelling from another room.

Posting about somebody instead of to them puts the conversation in front of an audience that cannot help. They will hear about it, because people always do, and now they are answering something said in public rather than something said to them, which makes it all harder than it was. The audience was usually the actual point.

Ask what you want before you post: to be understood by that person, or to be seen being right. If it is the first, send the message and skip the post. If it is the second, that is worth knowing about yourself.