You can think of blood moving round a body. It is not the most visible part of a person, and nobody watches it, but it has to keep moving. Stop it and everything stops with it. That is the picture the word carries: not the thing you notice, the thing you cannot do without.
可以想成血在身體裡繞著跑。它不是身上最顯眼的東西，平常也沒人在看它，但它必須一直流。一停下來，整個人就跟著停。這個字帶著的就是這個畫面：不是最醒目的那個，而是少了就不行的那個。兩種用法都站在這張圖上，差別只在那具身體是真的人，還是一間店、一座城。
From the word’s history
The word is simply life plus blood: the blood that life depends on. English has an older word built the same way, heart-blood.
這個字就是 life（生命）加 blood（血）拼起來的：性命所繫的那股血。英文裡還有一個用同樣方式造出來的老詞 heart-blood，意思一樣。
Wiktionary, "lifeblood"
登入就可以看每一支怎麼連回核心畫面。