Because man by nature lacks wings, even if you understand the theory of flight well--which is of course very important--training in safe areas, with actual time in the air, is critical. Indeed, it may even be necessary to learn from countless failures.
由於人們生來就沒有翅膀，因此除了嫻熟理論外，在空中的實戰經驗也相當重要，甚至必須從無數失敗中學習。