  Using this distinction between the two truths, the key insight of the ‘middle path’ may be expressed as follows. The ultimate truth about sentient beings is just that there is a causal series of impermanent, impersonal psychophysical elements. Since these are all impermanent, and lack other properties that would be required of an essence of the person, none of them is a self. But given the right arrangement of such entities in a causal series, it is useful to think of them as making up one thing, a person. It is thus conventionally true that there are persons, things that endure for a lifetime and possibly (if there is rebirth) longer. This is conventionally true because generally speaking there is more overall happiness and less overall pain and suffering when one part of such a series identifies with other parts of the same series. For instance, when the present set of psychophysical elements identifies with future elements, it is less likely to engage in behavior (such as smoking) that results in present pleasure but far greater future pain. The utility of this convention is, however, limited. Past a certain point—namely the point at which we take it too seriously, as more than just a useful fiction—it results in existential suffering. The cessation of suffering is attained by extirpating all sense of an ‘I’ that serves as agent and owner.