Why do we stop discussing smthing??

in normal conversations, this also takes place. a conversation seems to be going well and then, all of a sudden everyone goes quiet about it, and changes to another topic. there was just simply a different topic which floated which, everyone who has been participating, found another interesting one to talk about. turns in conversation like this is understandable as lots of ideas usually crop up in people's minds all of a suddent at most times. as for the discussions we have here on mylot, we just simply respond to a discussion at hand. if the poster and the responder find it worth delving into, they will be posting one comment after another for a while. but none will be persisting for so long. this is also understandable. we cannot go on talking about one thing here because, we are limited to communicating through posting comments. we cannot really expound so much this way.