Think of the plate you eat from every single day: bread, with butter on it. Nobody photographs it. Nobody talks about it afterwards. But take it away and the day stops working. That is the whole word — the plain thing underneath, the one that is not interesting and cannot be skipped.
From the word’s history
Bread and butter were the archetypal basic foods in the places where English developed, which is why English has a whole row of expressions built on them: daily bread, put bread on the table, earn one's bread, bread and water. The adjective grows out of that: the basic daily thing.
在英語發展的地方，麵包和奶油一向是最基本的日常食物，所以英文有一整排靠它們造出來的說法：daily bread、put bread on the table、earn one's bread、bread and water。形容詞的用法就是從這裡長出來的——最基本、天天都要有的那樣東西。
Wiktionary, "bread-and-butter"
登入就可以看每一支怎麼連回核心畫面。