If we know anything - it is to know that we know something. Knowing is the clearest indication that we exist. We understand almost all things by relating them to what we already know. We can only understand something if we can find it a home, if we can connect it to what we already understand.
Cognition works by association.
We know things because we can attach them to other things that we know. If knowledge can only work by attaching itself to that which is already there, necessarily there must be some point, however minuscule, of prior cognition to which that knowledge attaches. It's axiomatic then, that we cannot grasp that first point by ourselves - because that first point of cognition would have nothing to attach itself to. It's like starting a car. Once the car is running, the engine itself can generate enough power to sustain the cycle as long as the fuel lasts.