Having some sort of time limit on suffering makes it endurable. It’s the same way that running a marathon is tolerable because you know that it will eventually end. Every step gets you closer to relief.

I don’t think I’m a lightweight. I like to believe that I’m an expert on pain, thanks to hours devoted to close study of it during the births of my two children – one at home, one in hospital, neither with painkillers. Those experiences taught me that the most intense pain imaginable can be tolerated for a time, and that the way we experience that pain – empowering, terrifying, humbling – can vary dramatically.

And so even childbirth, the most painful thing commonly experienced, doesn’t work as an objective measure. There are other sorts of pain, harder to describe. Chronic or recurring pains are insidious. They eat away at energy, optimism, endurance, sense of self. More relevant than a measurement or even a description of pain, then, is the completely subjective impact is has on one’s thoughts, behaviour, and physical health. Pain above a “level 5” – moderate pain that dominates your thoughts and to which you cannot adapt, according to one scale designed to measure it – frequently results in temporary personality disorders. At higher levels that continue without relief, personality disorders are almost ubiquitous and suicide is common.

From Carlyn Zwarenstein’s Opium Eater: The New Confessions.