A child in its greed for love does not enjoy having to share the affection of its parents with its brothers and sisters; and it notices that the whole of their affection is lavished upon it once more whenever it arouses their anxiety by falling ill. It has now discovered a means of enticing out its parents' love and will make use of that means as soon as it has the necessary psychical material at its disposal for producing an illness.

Freud: on War, Sex and Neurosis (ed. 1947)