This used to be a cliche in the catering industry (there is another saying called "buy raw and sell cooked" ~). That is to say: (restaurant owner) cooks the raw materials and sells them to diners, and the net profit (earned) can reach more than half of its input cost! In other words, the catering industry is an industry with a large profit margin ~ ~ Later, this sentence was also "borrowed" by other industries to describe small profits. "one book is profitable" ~ ~