As in most things, progress in aviation has proceeded in distinct steps. A technical breakthrough resulting in a significant performance increment would be immediately adopted by all designers in the international competition for orders and recognition. One might recall the cantilever wing, the retractable landing gear, the jet engine, the swept wing, the delta wing and the supersonic wing. Performance and economics counted and if there were a few new handling or operational problems introduced— well, they would be attended to in good time. Reduced margins of stability were often accepted by test pilots; partly in their employer's interest, and partly because there is no easy answer to “what's good enough?” Handling qualities did have a substantial impact on economics, of course, but cause and effect were not yet clearly related.