Fatigue damage in aircraft structures, not wanted, but tolerated?

It has been a long way to arrive at the present state of the art about fatigue of structures and materials. Aircraft accidents and incidents were milestones. New concepts were proposed related to structural design, material selection, production techniques, inspection procedures and load spectra. Extensive research efforts have been spent. Our understanding of fatigue damage problems increased significantly. Simultaneously our tools to tackle problems have been developed to a high potential efficiency. And still, there are problems. The present paper is a personal impression of evaluating experience, design aspects, predictions and experiments associated with damage tolerance of aircraft structures.