A friend who used to do tech support told me that he learned that instead of asking "is it plugged in" it was better to ask the customer to unplug it and plug it back in. Then they might notice that it was unplugged but they don't have to admit it. I think about that a lot
A long, long time ago I (at that time junior sysadmin in training) had exactly this conversation with *the* managing director ...
And judging by his reaction, the network cable really wasn't plugged in