I know exactly why I was happy

In a vacuum all photons travel at the same speed. They slow down when travelling through air or water or glass. Photons of different energies are slowed down at different rates. If Tolstoy had known this, would he have recognised the terrible untruth at the beginning of Anna Karenina? ‘All happy families are alike; every unhappy family is unhappy in its own particular way.’ In fact it’s the other way around. Happiness is a specific. Misery is a generalisation. People usually know exactly why they are happy. They very rarely know why they are miserable. (…) Misery is a vacuum. A space without air, a suffocated dead place, the abode of the miserable. Misery is a tenement block, rooms like battery cages, sit over your own droppings, lie on your own filth. Misery is a no U-turns, no stopping road. Travel down it pushed by those behind, tripped by those in front. Travel down it at furious speed though the days are mummified in lead. It happens so fast once you get started, there’s no anchor from the real world to slow you down, nothing to hold on to. Misery pulls away the brackets of life leaving you to free fall. Whatever your private hell, you’ll find millions like it in Misery. This is the town where everyone’s nightmares come true.
(Jeanette Winterson – Written on the Body)