Purpose theorised as behaviour means the optimisation of a potential function, a sort of generalised utility. This may work more or less well as objective description, even if the theory needs to refract its notion of utility through evolutionary considerations which escape the individual, which escape anything the individual could rationally define in its own interest. Subjectively, however, purpose and utility turn into desire and enjoyment, and here the disparity, the décalage, between the two becomes glaring, even in self-reflection. You can't define enjoyment as the goal of your desire any more than you define desire as the seeking for enjoyment, but you also can't ignore the fact that they are deeply related, but in a way that evades exposure. Desire, enjoyment, and their disparity (which includes their occasional parity) are all equally complete embodiments of the subject. It's not that the subject bears a special relationship to the salient points of breakdown in the relations of these non-relatables, only that at those points it emerges in a doubled form as a non-object for reflection. Why would attention turn on itself since it knows no desire? There is nothing to motivate it, it can only ride the updrafts of desires that frustratedly seek their own forbidden objects. And every such object is more or less forbidden, there being no stable exchange between subjective and objective.