A long time ago, flying at night was risky and dangerous. Persons or businesses doing something illegal or of questionable ethics would fly at night because it was difficult to see the airplane at night. Smuggling something into the country is an example. Today, a fly by night operation refers to an illegal or unethical business.
不合法、不道德的經營
以前在夜晚飛行是很冒險且危險的，人們或者是公司再做一些不合法或者是有道德爭議的的交易時都會在夜晚進行，因為在夜晚飛行的飛機是很不容易被看見的，就好比是”非法走私”。