There are two great difficulties with which the professional soldier, sailor or airman has to contend in equipping himself as a commander. First, his profession is almost unique in that he may have to exercise it only once in a lifetime, if indeed that often. It is as if a surgeon had to practise throughout his life on dummies for one real operation; or a barrister appeared only once or twice in court toward the end of his career; or a professional swimmer had to spend his life practising on dry land for an Olympic championship on which the fortunes of his entire nation depended.
