I've forgotten something. Please help by reminding me!

A Classmate has posted something on my Notice Board (What's New?) page but the option for others to Add a Comment underneath isn't showing. I know there's a reason for this but I can't remember what it is and I'd like to tell him to do whatever it is to ensure that others can respond to what he's said, now and in future.

Thanks.

Has this classmate allowed comments in his profile settings?

That was it, John! I'll try not to forget again!
Thanks.