Against the suffering which may come upon one from human relationships the readiest safeguard is voluntary isolation, keeping oneself aloof from other people. The happiness which can be achieved along this path is, as we see, the happiness of quietness. Against the dreaded external world one can only defend oneself by some kind of turning away from it, if one intends to solve the task by oneself.

The Standard Edition of the Complete Psychological Works of Sigmund Freud (ed. 1961)