In the smallest nutshell I could possibly find, the Buddha taught that we cause our own suffering when we get attached to impermanent things. We cling to people, health and youth, even though we intellectually know that nothing lasts forever. That’s why the concept of “letting go” is so fundamental to Buddhism. Acknowledge everything that passes by like a cloud in the sky: some are beautiful, fluffy, and make us smile, while some are dark and cold—but they’re all impermanent.
