But more than that, even if every dream were well explained by the hypothesis of a double, and could not be explained otherwise, it would remain a question why men have attempted to explain them. Dreams undoubtedly constitute the matter of a possible problem. But we pass by problems every day which we do not raise, and of which we have no suspicion until some circumstance makes us feel the necessity of raising them. Even when the taste for pure speculation is aroused, reflection is far from raising all the problems to which it could eventually apply itself; only those attract it which present a particular interest. Especially, when it is a question of facts which always take place in the same manner, habit easily numbs curiosity, and we do not even dream of questioning them. To shake off this torpor, it is necessary that practical exigencies, or at least a very pressing theoretical interest, stimulate our attention and turn it in this direction. That is why, at every moment of history, there have been so many things that we have not tried to understand, without even being conscious of our renunciation. Up until very recent times, it was believed that the sun was only a few feet in diameter. There is something incomprehensible in the statement that a luminous disc of such slight dimensions could illuminate the world: yet for centuries men never thought of resolving this contradiction. The fact of heredity has been known for a long time, but it is very recently that the attempt has been made to formulate its theory. Certain beliefs were even admitted which rendered it wholly unintelligible: thus in many Australian societies of which we shall have occasion to speak, the child is not physiologically the offspring of its parents.[108] This intellectual laziness is necessarily at its maximum among the primitive peoples. These weak beings, who have so much trouble in maintaining life against all the forces which assail it, have no means for supporting any luxury in the way of speculation. They do not reflect except when they are driven to it. Now it is difficult to see what could have led them to make dreams the theme of their meditations. What does the dream amount to in our lives? How little is the place it holds, especially because of the very vague impressions it leaves in the memory, and of the rapidity with which it is effaced from remembrance, and consequently, how surprising it is that a man of so rudimentary an intelligence should have expended such efforts to find its explanation! Of the two existences which he successively leads, that of the day and that of the night, it is the first which should interest him the most. Is it not strange that the second should have so captivated his attention that he made it the basis of a whole system of complicated ideas destined to have so profound an influence upon his thought and conduct?