I commented on my Friend’s post but now I can’t see it! What’s happened?

Disappeared Comments and likes:

Very simple this one. The answer is almost certainly that the original poster has made a change that adversely affected your comment.

1. Deleted Original Post:
   Obviously if the Post is deleted then so are any comments, likes etc. related to it.
2. Deleted Comment:
   Yep, the original poster has the right to delete any comments from their posts.
3. Changed Visibility of Original Post:
   It could be that the original poster has altered the permissions on the original post. Perhaps a List that you are in (on the original poster’s account) or even you personally have been removed from those able to see the post.

Facebook make it a point of principle that changes to permissions/visibility or List membership are never advertised or visible to Friends, so you’ll never know the exact reason. Unless you ask the original poster.

They Can’t do that!:

Oh yes they can.
Now, even though you’ve interacted with the post and possibly even commented upon it, you don’t own it or your comment or even have many rights over it. Period.
Obviously a like or a comment can be just as embarrassing as any original post. But you’ll have to accept that in Facebook you have left almost all rights to that comment with the owner of the original post. If you want to delete it – do it ASAP. If the post is hidden from you later, tough. What is worse is that the comment will still be visible to the owner and anyone they decide to share it with!

Notes:

The reason for this is to ensure that there is a clear line drawn for permissions/ownership.
This means you can’t hold a post open by liking or commenting.

Activity Log:

Really, really annoyingly, Facebook will also hide the like/comment from you in your Activity Log. You now have no way to check what you said or indeed any record that you did anything in the first place.