Picture people shut inside somewhere safe — a town, an airbase, a hotel room in a city you do not know. They open the door, go out, do one thing, and come back in. That is the whole word. Two parts matter. The place you set out from is always there in the background, and you are expected to return to it. So a sortie is never a journey that ends somewhere else; it is a loop that starts and finishes at the same door. Because each loop is complete, you can count them.
From the word’s history
Wiktionary says the English word is borrowed from French sortie, the feminine past participle of sortir, to go out, and before that from Latin sortiri. So the word's literal content is simply the going-out. Everything on this page is that one act, put in a different setting each time.
依 Wiktionary，這個字借自法文 sortie，是動詞 sortir（出去）的陰性過去分詞，再往前是拉丁文 sortīrī。也就是說，這個字字面上就只有「出去」這件事。這一頁上的每個用法，都是把同一個動作換到不同的場景裡而已。
Wiktionary, "sortie"
登入就可以看每一支怎麼連回核心畫面。