@jascha recently I needed to give my phone number to a student.
They came back to me "your number doesn't work"
I double checked it, it was correct.
"I can't find you though?"
I am looking like a car in that moment, saying "what do you mean, you can't find me?"
They were typing my number directly into WhatsApp. It did not even occur to them that someon could just ... not use WhatsApp.