Imagine you were designing an online messaging system. On your system, people could write messages, and other people could reply to them. And people could reply to the replies, and so on.
So imagine you had a sequence of 5 messages,  to , where each is a reply to the last. In what order would you display them on the screen? I’d like you to think about that for a bit before you scroll down…
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So having thought about it, you might decide on the order 1, 2, 3, 4, 5. This would be sensible because it it chronological order.
Or you might decide on most-recent-first, i.e. 5, 4, 3, 2, 1, to give prominence to the most recent message.
One order I suspect you would not choose is 5, 3, 1, 2, 4. Unless that is you were Jack Dorsey and were running Twitter:
Here the original message (1) is from Stephanie Hurlbert, to which Alex Afshar replied (2). Then Gravis McElroy replied with a message (3) and a whole thread (4). Finally, craignicol reposted it (5).
What an absurdity of user interface design.