Craving is wanting the impossible, that’s why it’s painful. A typical example of craving is heartbreak after a romantic breakup. A more subtle example of craving is wanting something because you think it will make you happy. That’s also wanting the impossible, because you know very well that your happiness won’t last long after you get it.

Which is why enlightened beings never crave, they have suffered the ultimate heartbreak and thus, they are always happy. They only want what’s possible, and if it turns out to be impossible, they stop wanting it.