What is Typing Indicators?
The 'someone is typing' indicator creates an open loop: you know a reply is coming, so you keep waiting on the screen instead of closing the app.
Where it comes from
Early Instant Messaging (1997)
How it hooks you
Exploits social anticipation: an unresolved 'reply incoming' signal holds your attention on an otherwise empty screen.
How to resist it
Disable typing indicators where your app allows it, or put the phone down after sending a message.