If you think about it carefully, you will see that this comes from the fact that the opposite – total evil – was not brought into being at once. Initially there was only a certain concealment of perfection. What remained of the perfection that was not completely concealed was good, while what was lacking from the initial perfection was bad. With the first concealment, a great deal of the initial perfection remained, while the deficiency was minimal.
We could even say that there was no actual deficiency but only a preparation that would eventually lead to the development of evil, inasmuch as there was now a state of concealment, whereas evil would not have developed from perfection at all. Thus, as stated earlier, there was as yet no deficiency but only a state of concealment. Afterwards a second concealment occurred, but even so, much of the initial perfection remained while the deficiency was still minor.