Appeals for donations to help people in a crisis may initially meet with large responses but repeated frequent appeals may soon result in little or no response. Charities know that extraordinary success of one appeal is unlikely to be repeated by a similar one. Images of famine or flood victims become too familiar and people become inured. "Compassion fatigue" can sap public sympathy. Causes become fashionable and unfashionable. Long-term relief projects are in danger of becoming out of favour with the public and thereby may be terminated prematurely.