The finest explanation I've read so far. In Margaret Atwood's post-climate-catastrophic novel Oryx and Crake. Snowman, a battered survivor is slowly losing his mind and memories.
"What is toast?" says Snowman to himself, once they've run off. Toast is when you take a piece of bread - What is bread? Bread is when you take some flour - What is flour? We'll skip that part, it's too complicated. Bread is something you can eat, made from a ground-up plant and shaped like a stone. You cook it . . . Please, why do you cook it? Why don't you just eat the plant? Never mind that part - Pay attention. You cook it, and then you cut it into slices, and you put a slice into a toaster, which is a metal box that heats up with electricity - What is electricity? Don't worry about that. While the slice is in the toaster, you get out the butter - butter is a yellow grease, made from the mammary glands of - skip the butter. So, the toaster turns the slice of bread black on both sides with smoke coming out, and then this "toaster" shoots the slice up into the air, and it falls onto the floor . . .
"Forget it," says Snowman. "Let's try again." Toast was a pointless invention from the Dark Ages. Toast was an implement of torture that caused all those subjected to it to regurgitate in verbal form the sins and crimes of their past lives. Toast was a ritual item devoured by fetishists in the belief that it would enhance their kinetic and sexual powers. Toast cannot be explained by any rational means.
Toast is me.
I am toast."