Picture a single line drawn from birth to death — the whole stretch, seen from the outside as one measured length. Because that length is the longest one a person gets, English also uses it as a ruler: if something only happens once in that whole line, it is rare; if it will not happen even in that whole line, it will never happen.
可以想成：從出生畫到死亡的一整條線，從外面看就是「一段有長度的時間」。因為這是一個人能拿到最長的一段，英文也順手拿它當尺來量：一件事在整條線上只出現一次，就是難得；一件事連整條線都等不到，就是永遠不會。
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，摘錄並精簡格式，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
lifetimenoun/ˈlaɪf.taɪm/
- 1
The duration of the life of someone or something.
- a project that will take many human lifetimes to complete
- the operational lifetime of an aircraft component
- 2
informalA long period of time.
- I've been waiting a lifetime for a train.
摘錄自 英文維基詞典 English Wiktionary，已精簡格式；依 CC BY-SA 4.0 授權使用，改動後的內容同樣以此授權提供。