Something happens in the brain when fatalities reach such high numbers, say psychologists who have studied genocides and mass disasters. The casualties become like a mountain of corpses that has grown so large it becomes difficult to focus on the individual bodies.

With the coronavirus in particular, experts say, the deaths have been hidden from sight even from friends and family — the human cost sequestered in hospitals and nursing homes.

“Sometimes I think, if only others could see what we see every day,” said Joan Schaum, a hospice nurse who has spent the past year caring for the dying in Lancaster, Pa.

“Other times,” she said, “I think, no one should have to see the amount of death and suffering going on right now. It changes you. It stays with you.”