One way to hold this word: you already walked out, the door is still there, and now you walk back in. The weight is not on going in — it is on this being the second time. Something always came before it: you left a job, a market, a piece of land, or the Earth's air. So the word carries a line that goes out and then comes back.
可以想成一個畫面：你已經走出去了，那道門還在，然後你又走了回去。重點其實不在「進去」，而在「這是第二次」。前面一定有一段離開——離開職場、離開市場、離開一塊地，或離開地球的空氣層。所以 re-entry 身上總是帶著一條來回的線：出去，再回來。也因為這樣，它常常帶著一點「終於回來了」的分量。
From the word’s history
The source entry records the word as re- plus entry, that is, an entry that happens again.
來源資料記載這個字由 re-（再一次）加 entry（進入）組成，字面就是「再發生一次的進入」，正好對上它今天所有用法裡那個「第二次」的重點。
Wiktionary, "re-entry"
登入就可以看每一支怎麼連回核心畫面。