Of such things, they see that those which quickly come to pass--that is, quickly come into existence--quickly also disappear; whereas they regard as more difficult of accomplishment--that is, not so easily brought into existence--those things which they conceive as more complicated.
However, to do away with this misconception, I need not here show the measure of truth in the proverb, "What comes quickly, goes quickly," nor discuss whether, from the point of view of universal nature, all things are equally easy, or otherwise: I need only remark that I am not here speaking of things, which come to pass through causes external to themselves, but only of substances which (by Prop.

vi.) cannot be produced by any external cause.

Things which are produced by external causes, whether they consist of many parts or few, owe whatsoever perfection or reality they possess solely to the efficacy of their external cause; and therefore their existence arises solely from the perfection of their external cause, not from their own.

Contrariwise, whatsoever perfection is possessed by substance is due to no external cause; wherefore the existence of substance must arise solely from its own nature, which is nothing else but its essence.

Thus, the perfection of a thing does not annul its existence, but, on the contrary, asserts it.
Imperfection, on the other hand, does annul it; therefore we cannot be more certain of the existence of anything, than of the existence of a being absolutely infinite or perfect--that is, of God.