Thresholds of pain, indignity and incapacity are entirely personal.

It is now possible to quantify people's levels of happiness pretty accurately by asking them, by observation, and by measuring electrical activity in the brain, in degrees from terrible pain to sublime joy.

One in six people suffer depression or a chronic anxiety disorder. These are not the worried well but those in severe mental pain with conditions crippling enough to prevent them living normal lives.

The strongest predictor of unhappiness is anyone who has had a mental illness in the last 10 years. It is an even stronger predictor of unhappiness than poverty - which also ranks highly.

My mother begged doctors to end her life. She was beyond the physical ability to swallow enough of the weak morphine pills she had around her. When she knew she was dying I promised to make sure she could go at a time of her choosing, but it was impossible. I couldn't help.

How do you make any sense of history, art or literature without knowing the stories and iconography of your own culture and all the world's main religions?