Priority of Dasein has to do with why we should concentrate our efforts in understanding Dasein, over any other Ontic being. Just so happens that the entity that is dasein, at least Indo-European ones, are projecting Being (which is the ontological priority) onto everything including themselves (which is the ontic priority). Dasein also has an understanding of entities with a character other than its own, and thus it is uniquely situated to produce ontologies of other things (which is the ontico-ontological priority). Since Being is intelligibility it is the intelligibility of ontic things in the world, including other people. So this last priority which is the basis of any ontology what-so-ever is the priority of Dasein as the entity that understands the world.

Here then Heidegger refers to himself when he says that the roots of the existential analytic is ultimately existentiell and thus ontical with respect to his own dasein. But when this is raised to a philosophcial level then we consider dasein in general based on our own dasein and generalizing to understand the existentiality of existence from our familiarity with our own existentiell situation. This is as much to recognize that Heideggers development of the existential of Dasein will be colored by his own existentiell considerations. But the founding of the ontological problematic is general despite its unique origins in a particular dasein, i.e. Heidegger.

When we look at ourselves as entities as if from the outside we dive into the ontic. But when we look at ourselves as being situated in the world we have some responsibility for we find our existentiell characteristics. But because we are human and within an Indo-European culture with Being this allows us to undertake an existential analytic based on our unique existentiell characteristics we know first hand concerning human existence by living it. We generalize to others what we ourselves discover about ourselves and in the process come to know more about the character of dasein in general which is ontological (at least for us as Indo-Europeans). Thus we project the a priori nature of the ontological from which all ontologies must come based on our own existential analytic rooted in our existentiell experience as one ontic entity among others, but special in that we project the character of the others out of ourselves in an ecstasy that constitutes the situation we find ourselves within, and so we a priori constitute ourselves. The existential analytic is about how that process of a priori synthetic constitution works.