The complicated structure of our mental apparatus admits, however, of a whole series of other kinds of influence. The gratification of instincts is happiness, but when the outer world lets us starve, refuses us satisfaction of our needs, they become the cause of very great suffering. So the hope is born that by influencing these impulses one may escape some measure of suffering. This type of defence against pain no longer relates to the sensory apparatus; it seeks to control the internal sources of our needs themselves. An extreme form of it consists in annihilation of the instincts, as taught by the wisdom of the East and practised by the Yogi. When it succeeds, it is true, it involves giving up all other activities as well (sacrificing the whole of life), and again, by another path, the only happiness it brings is that of peace. The same way is taken when the aim is less extreme and only control of the instincts is sought. When this is so, the higher mental systems which recognize the reality-principle have the upper hand. The aim of gratification is by no means abandoned in this case; a certain degree of protection against suffering is secured, in that lack of satisfaction causes less pain when the instincts are kept in check than when they are unbridled. On the other hand, this brings with it an undeniable reduction in the degree of enjoyment obtainable. The feeling of happiness produced by indulgence of a wild, untamed craving is incomparably more intense than is the satisfying of a curbed desire. The irresistibility of perverted impulses, perhaps the charm of forbidden things generally, may in this way be explained economically.