There's no place that proves we shouldn't have jet packs better than the grocery store.
Not because there are a lot of crashes, but because in no other place do people act as if they are alone when surrounded by other people.
Why else would someone park their cart on one side of the aisle and then stand in the space between it and the other side of the aisle to browse the shelves and single-handedly block an entire aisle? Why else would someone abruptly turn around without even a glance to see if anyone else is in the space they want to enter? In the grocery store, the cart is your own personal world, the store is your private freeway, and other carts are not other people, with hopes, fears and dreams of their own, but obstacles that are in your - your! - way.
It's easy to fall into cart rage in such situations. Too easy, to snarl at the idiot who can't decide which way they want to go, or which aisle has the items they want. You can build up a head of steam even in the moments before you get a cart as the person ahead of you blocks your way to grab one.
But that's just not healthy. Better by far to stand back, take a deep breath, and smile at the absurdity of the oblivious.
Better to nod to yourself with wisdom, knowing that this, this is why we can't have jet packs.