What have you not understood? What do you know about the same subject....Well said @cryptorg. The idea, as you so aptly state, is to get involved, share in the perspective of the author, relate to it, suggest alternatives. What could have been said/done differently? What is your take on the characters, if it is a story? What are your thoughts on the theme, if it is a poem? What do you make of the proposition, if the author is suggesting a new way to trade in cryptocurrency.

Such discussions are what make the cut, other than insincere only-attention-seeking 'great post', 'nice writing' ,'thanks for sharing' kind of posts. These kind of short comments should only come as a salutation or for signing off your elaborate comment.