Here libido and ego-interest share the same fate and have once more become indistinguishable from each other. The familiar egoism of the sick person covers them both. We find it so natural because we are certain that in the same situation we should behave in just the same way. The way in which the readiness to love, however great, is banished by bodily ailments, and suddenly replaced by complete indifference, is a theme which has been sufficiently exploited by comic writers.
...observe the difference between your attitude to illusions and mine. You have to defend the religious illusion with all your might. If it becomes discredited - and indeed the threat to it is great enough - then your world collapses. There is nothing left for you but to despair of everything, of civilization and the future of mankind. From that bondage I am, we are, free. Since we are prepared to renounce a good part of our infantile wishes, we can bear it if a few of our expectations turn out to be illusions.
We believe that it is possible for scientific work to gain some knowledge about the reality of the world, by means of which we can increase out power and in accordance with which we can arrange our life. If this belief is an illusion, then we are in the same position as you. But science has given us evidence by its numerous and important successes that it is no illusion.
The view is often defended that sciences should be built up on clear and sharply defined basal concepts. In actual fact no science, not even the most exact, begins with such definitions. The true beginning of scientific activity consists rather in describing phenomena and then in proceeding to group, classify and correlate them.