The Buddha suggested the core of his teaching in one short sentence: "I teach dukkha [suffering or reactivity or a sense of unsatisfactoriness] and the cessation of dukkha.” We explore this teaching in several ways. We see how the Buddha had multiple ways of talking about dukkha, with only, I suggest, the understanding of dukkha as reactivity, making sense of what the end of dukkha means. Dukkha as reactivity is explicated especially in two teachings, the Two Arrows and Dependent Origination. We look at the meaning of reactivity and how it manifests in our experience. We also see how reactivity can often be enmeshed with insight, such it makes sense to speak of transforming reactivity rather than simply suppressing it. We then explore five ways of practicing with reactivity. The talk is followed by discussion.