(1)Display blanking for a few seconds (no cases at all in operational service in millions of hours). Or a few minutes or until landing
(2)at precisely the wrong moment (must happen at critical phase of flight. Or at any time at cruising altitude. Have you tried flying visually at 41000 feet?
(3) Simultaneously to BOTH PF and PNF displays) and
(4)Simultaneously with a standby systems failure (ever seen standby instruments fail?) Yep, I have.
(5) IMC see (2)
(6) with a pilot who cannot cope (vanishingly small chance ). Some can hardly cope WITH the displays working.