Per contemporary and post war reports, the unending tsunamis of T-34s and Shermans were hugely demoralizing. On the occasions where their complex systems didn't immobilize them, even the most German armor would get swarmed under. The joke among the Germans on the Western Front was that a Panther or Tiger would easily destroy eight Shermans - but there was always a 9th Sherman that would take out the German tank. "Crunch all you want, we'll make more" was a concept that is hugely demoralizing on the receiving end - and despite the glurge about all Shermans being deathtraps, the stats show the Sherman was actually one of the safer tanks to be in during the war. So you'd have an Allied crew lose their track to hostile fire, go back to the depot, get another Sherman - and in some cases, the very next or same day, take their new Sherman back and kill what destroyed their last one.
That said, at the end of the war the most feared Allied machine on the Western Front was the M18 Hellcat, because it could shoot and scoot - and it could literally circle strafe German tanks faster than the tanks could turn their turrets. It was like trying to fight speedy ghosts that could appear from any bearing on the battlefield, rape the German armor, disappear before any response could be organized then appear from a completely different side to repeat the process over and over. Apparently those things caused German officers' nightmares, even worse than the tsunamis of Shermans.
The Eastern Front was a rather different matter. The Germans were too busy seeing things like this heading for them to be scared of one particular machine:
If you're in the German army at that point, seeing that mass of metal and troops heading for you? Yeah, you're screwed. In case anyone is wondering, those are IS-2 heavy tanks in the center, with the monstrous 122mm guns that nothing Germany had could keep out.