[cassowary]

The point was that being displayed on my screen doesn't mean I read it. For instance, I have a problem where sometimes I'll log in to my phone and an app will be active. I don't want that app; I need to do a bank transaction. But now someone thinks their message has been read, when so far from reading it I don't even know it exists! It was just displayed on my screen for half a moment when my eyes and my attention was somewhere else. (Another common problem I have is when I send a message, and then they reply so fast that the message arrives at about the same time as I'm trying to return to the homescreen to ensure I get a notification when the message arrives. Well unfortunately the message arrived first, got marked as read and no notification exists. After twenty minutes I realise what happens but maybe I've already offended someone by "reading" their message and ignoring it.)

Delivered vs read is only accurate if you have an eye tracker.