Can you with stand that silence?

I'm talking about the sort of thing your boss might do just after the moment you've asked for a raise, or that a salesman may try on you. If you just listen from 1:46 onwards in the below video, you'll hear Quintin Tarantino describe how it happened to him once.

I haven't quite put my finger on why it is that holding out this silence is so much harder to do in reality. All you have to do is shut up and stay still. It should be very easy!

Has anyone had experiences of this sort?