Ética, Parte V, Proposição 6

The mind understands all things to be necessary (I. xxix.) and to be determined to existence and operation by an infinite chain of causes; therefore (by the foregoing Proposition), it thus far brings it about, that it is less subject to the emotions arising therefrom, and (III. xlviii.) feels less emotion towards the things themselves. Q.E.D.

The more this knowledge, that things are necessary, is applied to particular things, which we conceive more distinctly and vividly, the greater is the power of the mind over the emotions, as experience also testifies. For we see, that the pain arising from the loss of any good is mitigated, as soon as the man who has lost it perceives, that it could not by any means have been preserved. So also we see that no one pities an infant, because it cannot speak, walk, or reason, or lastly, because it passes so many years, as it were, in unconsciousness. Whereas, if most people were born full--grown and only one here and there as an infant, everyone would pity the infants; because infancy would not then be looked on as a state natural and necessary, but as a fault or delinquency in Nature; and we may note several other instances of the same sort.