 The great difficulty for such a position is accounting for apparent continuities. The standard Buddhist explanation is that usually, when things go out of existence, they are replaced in the next moment by new elements of the same kind, and these streams of entities cause the appearance of continuity. Modern interpreters often illustrate the point with the example of the apparent motion on a movie screen being caused by a quick succession of stills. This is said to be the case with the many entities that appear to make up the continuous self, and of course this was the main reason the Buddha affirmed his doctrine of impermanence in the first place. Yet for some phenomena, to call their continuity merely apparent causes philosophical problems, even for Buddhists. Consequently, Vasubandhu, like his Sarvāstivāda forbears, was repeatedly preoccupied with the need to account for continuity.