'People struggle to understand grief, but it is a byproduct of love'

Mary-Frances O’Connor is an associate professor at the University of Arizona, where she leads the grief, loss and social stress (Glass) lab, investigating the effects of grief on the brain and the body.

Why do humans grieve? One of the earliest things that we learn is that we’re all going to die, so when it happens, why is it such a shock?
I think a lot of people historically have struggled to understand why there is grief, and in a funny sort of way, it is a byproduct of love. What I mean by that is, when we bond with another person, our spouse or our child, the way that gets encoded includes this belief that they will always be there for us and we will always be there for them. This is why we can kiss our partner goodbye in the morning and go on our separate ways to work, with the deep knowledge that we will come back together again at the end of the day.

But in the very unusual, thank goodness, cases where that loved one dies, the brain is able to consult our memory of being there at the bedside or getting that terrible phone call, but those two streams of information conflict for a long time. This often leads people to saying things like: “I’m not crazy. I know they’ve died, but it really feels like they’re just going to walk through the door again.”

So what is going on in the brain when people “see” their deceased loved one?
They know it’s irrational and yet it is surprisingly real for them. There are lots of people who will believe in an afterlife, but as a neuroscientist, my take is that the brain is a prediction machine. The heart is there to pump blood around your body. Your brain is there to predict what’s about to happen so that you can prepare for it. Because of this, we are always living in our predicted world. We’re living in two worlds at the same time, our predicted world and the real world, and in some circumstances, those don’t match up.

https://www.theguardian.com/science/2022/mar/05/mary-frances-oconnor-the-grieving-brain-grief-psychology