Tonglen is a Tibetan mind-training practice that runs the natural direction of self-interest in reverse. On the in-breath you take in someone's suffering — visualised as hot, dark, heavy smoke — and on the out-breath you send them relief, coolness, light. The instruction is to start where it is easy, someone you love, and then work outward to strangers, and finally to the person you actively resent, which is where the practice stops being pleasant. Pema Chodron popularised it in the West with an honest warning attached: the practice is not designed to make the practitioner feel good, and if it is comfortable, it is probably not being done.