All scientific work is incomplete—whether it be observational or experimental. All scientific work is liable to be upset or modified by advancing knowledge. That does not confer upon us the freedom to ignore the knowledge we already have, or to postpone the action that it appears to demand at a given time. As quoted in Sir Austin Bradford Hill, The Environment and Disease; Association or Causation? Proceeding of the Royal Society of Medicine, 1965, 58, 295. 10.1177/003591576505800503.