Answered in example sentence
It is a great misfortune to be alone, my friends; and it must be believed that solitude can quickly destroy reason, since you have found this poor creature in such a state!""But, captain," asked Herbert, "what leads you to think that the brutishness of the unfortunate man began only a few months back?""Because the document we found had been recently written," answered the engineer, "and the castaway alone can have written it."