Have you ever come across a post that's received quite a few comments, but you can't quite tell who's talking to whom?
Isn't it a bit like being in a big room of people where everyone is involved in their own small conversations... but for some odd reason, aren't necessarily looking at the person they're talking to? For all you know, they could be talking to themselves, the person directly behind them, or someone on the other side of the room.
To apply this metaphor to Multiply, for example, the latest reply at the bottom of the page -- say, the fifteenth -- that simply reads "Cool!" could potentially be posted in reference to the original posting, or something insightful in any of the previous fourteen comments.

How can this sort of thing be avoided? Thanks for asking!
There are two major ways around this:
- When replying to a specific comment already left on a posting, be sure to use the dedicated "reply" link that you'll find next to the particular comment. (Note the blue links in the screenshot to the right.)
Then, be sure to quote an appropriate portion of the comment to give people an idea of the comment to which you intend to reply. This is polite to do, but not usually necessary when you...
- Use "Threaded" comment view! When you do so, you'll see comments arranged in a logical order, showing you specifically which comments were left in reply to which! You can clearly see that each indented comment is a reply to the next left-most one, often the one above it.
If you've never used it before, it looks a little like this:

This is a great way to keep track of conversations, but comments will only appear in this manner if those involved in the conversation used the dedicated reply links mentioned above when posting their replies.
(Additionally, Threaded mode doesn't support Live RepliesTM just yet.)
So there you have it. If you have trouble making sense of a conversation, you may want to switch your comment view to "Threaded," at least temporarily. And remember to use those "reply" links when responding to existing comments!